Conductive lithium storage electrode

ABSTRACT

A compound comprising a composition A x (M′ 1−a M″ a ) y (XD 4 ) z , A x (M′ 1−a M″ a ) y (DXD 4 ) z , or A x (M′ 1−a M″ a ) y (X 2 D 7 ) z , (A 1−a M″ a ) x M′ y (XD 4 ) z , (A 1−a M″ a ) x M′ y (DXD 4 ) z , or (A 1−a M″ a ) x M′ y (X 2 D 7 ) z . In the compound, A is at least one of an alkali metal and hydrogen, M′ is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, molybdenum, and tungsten, M″ any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen, carbon, or a halogen, 0.0001&lt;a≦0.1, and x, y, and z are greater than zero. The compound can be used in an electrochemical device including electrodes and storage batteries.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/901,463, filed Sep. 17, 2007, now U.S. Pat. No. 8,148,013, which is acontinuation of U.S. patent application Ser. No. 10/329,046, filed onDec. 23, 2002, now U.S. Pat. No. 7,338,734, which claims priority under35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/343,060,filed on Dec. 21, 2001, U.S. Provisional Application Ser. No.60/388,721, filed on Jun. 14, 2002, and U.S. Provisional ApplicationSer. No. 60/412,656, filed on Sep. 20, 2002, the disclosures of whichare herein incorporated by reference.

GOVERNMENTAL SUPPORT

This invention was made with government support under Grant NumberDE-FG02-87ER45307 awarded by the Department of Energy. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to transition metal polyanion oxidesthat can be used as alkali ion combined materials and more particularlyto lithium-ion intercalating structures that can be used aselectrochemical compounds.

2. Description of the Related Art

The published literature contains many references by those skilled inthe art to the insulating nature of these compounds, and the limitationson their utility as battery storage materials thereby created. Forexample, Gaubicher et al. (J. Gaubicher, T. Le Mercier, Y. Chabre, J.Angenault, and M. Quarton, “Li/β-VOPO₄: A New 4 V System for LithiumBatteries,” J. Electrochem. Soc., 146[12] 4375-4379 (1999)) comment withrespect to the NASICON compounds that “unfortunately, the anionic unitstend to isolate the transition elements, which consequently leads to lowelectronic conductivity.”

In “Approaching Theoretical Capacity of LiFePO₄ at Room Temperature atHigh Rates,” H. Huang, S.-C. Yin and L. F. Nazar, Electrochem. Sol. St.Lett., 4[10] A170-A172 (2001), explain that “however, owing to theirvery poor conductivity, initial reports indicated that Li⁺ can only bepartially extracted/inserted at room temperature at modest rates.” And,in “Issues and challenges facing rechargeable lithium batteries,” J.-M.Tarascon and M. Armand, Nature, 414, 359-367 (2001), note that withrespect to these compounds that “one of the main drawbacks with usingthese materials is their poor electronic conductivity, and thislimitation had to be overcome through various materials processingapproaches, including the use of carbon coatings, mechanical grinding ormixing, and low-temperature synthesis routes to obtain tailoredparticles.”

Proposed solutions to the poor electronic conductivity have typicallyfocused entirely on coating with carbon or adding a significant excessof carbon during synthesis. Coating with carbon has been described by N.Ravet et al. in “Improved iron-based cathode materials,” Abstr. No. 12,ECS Fall meeting, Hawaii, 1999 and by Morcrette et al. in M. Morcrette,C. Wurm, J. Gaubicher, and C. Masquelier, “Polyanionic structures asalternative materials for lithium batteries,” Abstr. No. 93, Li BatteryDiscussion Meeting, Bordeaux, Archachon, 27 May-1 Jun. 2001.Co-synthesizing with carbon has been discussed by H. Huang et al. at theUniv. of Waterloo and by Yamada et al. at the Electrochemical SocietyFall Meeting, San Francisco, Calif., September 2001. However, theaddition of carbon as a conductive additive can lower the gravimetricand volumetric capacity of the storage material. In some instances,about 20 wt % carbon is added to the electrode formulation(approximately 30% by volume). This significant volume of carbon doesnot typically store lithium storage at the potentials at which thepolyanion compounds store lithium.

It is therefore clear and widely acknowledged by those skilled in theart that poor electronic conductivity is, firstly, an inherent featureof the lithium-metal-polyanion compounds discussed herein, and secondly,that this inherent feature limits the applicability of the materials inlithium storage applications, including lithium battery electrodes,especially at temperatures near room temperature. While publishedliterature and patents describe the addition of various metal additivesto such compounds, they are silent as to whether the critical andenabling property of improved electronic conductivity can be obtained.

SUMMARY OF THE INVENTION

The invention provides compounds, methods of forming compounds,electrodes that comprise compounds and storage battery cells thatinclude an electrode that comprises a compound.

In one set of embodiments, a compound is provided. The compoundcomprises a composition A_(x)(M′_(1−a)M″_(a))_(y)(XD₄)_(z),A_(x)(M′_(1−a)M″_(a))_(y)(DXD₄)_(z), orA_(x)(M′_(1−a)M″_(a))_(y)(X₂D₇)_(z), wherein A is at least one of analkali metal or hydrogen, M′ is a first-row transition metal, X is atleast one of phosphorus, sulfur, arsenic, boron, aluminum, silicon,vanadium, molybdenum and tungsten, M″ is any of a Group IIA, IIIA, IVA,VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is atleast one of oxygen, nitrogen, carbon, or a halogen, 0.0001<a≦0.1, and xis equal to or greater than 0, y and z are greater than 0 and havevalues such that x, plus y(1−a) times a formal valence or valences ofM′, plus ya times a formal valence or valence of M″, is equal to z timesa formal valence of the XD₄, X₂D₇, or DXD₄ group. In some of theseembodiments, the compound has a conductivity at 27° C. of at least about10⁻⁸ S/cm. In some of these embodiments, the compound has a specificsurface area of at least 15 m²/g. In some of these embodiments, thecompound crystallizes in an ordered or partially disordered structure ofthe olivine (A_(x)MXO₄), NASICON (A_(x)(M′,M″)₂(XO₄)₃), VOPO₄,LiFe(P₂O₇) or Fe₄(P₂O₇)₃ structure-types, and has a molar concentrationof the metals (M′+M″) relative to the concentration of the elements Xthat exceeds the ideal stoichiometric ratio y/z of the prototypecompounds by at least 0.0001.

In another set of embodiments, a compound is provided. The compoundcomprises a composition (A_(1−a)M″_(a))_(x)M′_(y)(XD₄)_(z),(A_(1−a)M″_(a))_(x)M′_(y)(DXD₄)_(z), or(A_(1−a)M″_(a))_(x)M′_(y)(X₂D₇)_(z), wherein A is at least one of analkali metal or hydrogen, M′ is a first-row transition metal, X is atleast one of phosphorus, sulfur, arsenic, boron, aluminum, silicon,vanadium, molybdenum and tungsten, M″ any of a Group IIA, IIIA, IVA, VA,VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is at leastone of oxygen, nitrogen, carbon, or a halogen, 0.0001<a≦0.1, and x, y,and z are greater than zero and have values such that (1−a)_(x) plus thequantity ax times the formal valence or valences of M″ plus y times theformal valence or valences of M′ is equal to z times the formal valenceof the XD₄, X₂D₇ or DXD₄ group. In some of these embodiments, thecompound has a conductivity at 27° C. of at least about 10⁻⁸ S/cm. Insome of these embodiments, the compound has a specific surface area ofat least 15 m²/g. In some of these embodiments, the compoundcrystallizes in an ordered or partially disordered structure of theolivine (A_(x)MXO₄), NASICON (A_(x)(M′,M″)₂(XO₄)₃), VOPO₄, LiFe(P₂O₇) orFe₄(P₂O₇)₃ structure-types, and has a molar concentration of the metals(M′+M″) relative to the concentration of the elements X that exceeds theideal stoichiometric ratio y/z of the prototype compounds by at least0.0001.

In another embodiment, a compound is provided. The compound comprises acomposition (A_(b−a)M″_(a))_(x)M′_(y)(XD₄)_(z),(A_(b−a)M″_(a))_(x)M′_(y)(DXD₄)_(z), or(A_(b−a)M″_(a))_(x)M′_(y)(X₂D₇)_(z), wherein A is at least one of analkali metal or hydrogen, M′ is a first-row transition metal, X is atleast one of phosphorus, sulfur, arsenic, boron, aluminum, silicon,vanadium, molybdenum and tungsten, M″ any of a Group IIA, IIIA, IVA, VA,VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is at leastone of oxygen, nitrogen, carbon, or a halogen, 0.0001<a≦0.1, a≦b≦1, andx, y, and z are greater than zero and have values such that (b−a)_(x)plus the quantity ax times the formal valence or valences of M″ plus ytimes the formal valence or valences of M′ is equal to z times theformal valence of the XD₄, X₂D₇ or DXD₄ group. In some of theseembodiments, the compound has a conductivity at 27° C. of at least about10⁻⁸ S/cm. In some of these embodiments, the compound has a specificsurface area of at least 15 m²/g. In some of these embodiments, thecompound crystallizes in an ordered or partially disordered structure ofthe olivine (A_(x)MXO₄), NASICON (A_(x)(M′,M″)₂(XO₄)₃), VOPO₄,LiFe(P₂O₇) or Fe₄(P₂O₇)₃ structure-types, and has a molar concentrationof the metals (M′+M″) relative to the concentration of the elements Xthat exceeds the ideal stoichiometric ratio y/z of the prototypecompounds by at least 0.0001.

In another set of embodiments, methods of forming a compound areprovided. The methods include mixing an alkali metal or hydrogen salt, afirst-row transition metal salt, a salt of at least one of phosphorus,sulfur, arsenic, silicon, aluminum, boron, vanadium, molybdenum andtungsten, and a salt of any of a Group IIA, IIIA, IVA, VA, VIA, VIIA,VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal; milling the mixture; andheat treating the mixture at a temperature between 300-900° C.

In another set of embodiments, methods of doping a material to form alithium or hydrogen storage compound are provided. The methods includeselecting a starting material to be doped, in conjunction with selectionof milling equipment comprising a dopant for doping the startingmaterial at a predetermined level of dopant. The methods further includemilling the starting material in the milling equipment; and recoveringfrom the milling step a material suitable for forming a lithium orhydrogen storage compound comprising the starting material doped withthe dopant at the predetermined level.

In another set of embodiments, an electrode comprising a lithium storagecompound is provided. The electrode can comprise any of the compoundsdescribed above and has a material energy density (i.e., voltage vs. Li×charge capacity) that while: charging or discharging at a rate ≧30 mAper g of storage compound, is greater than 350 Wh/kg; or, charging ordischarging at a rate ≧150 mA per g of storage compound, is greater than280 Wh/kg; or, charging or discharging at a rate ≧300 mA per g ofstorage compound, is greater than 270 Wh/kg; or, charging or dischargingat a rate ≧750 mA per g of storage compound, is greater than 250 Wh/kg;or, charging or discharging at a rate ≧1.5 A per g of storage compound,is greater than 180 Wh/kg; or, charging or discharging at a rate ≧3 Aper g of storage compound, is greater than 40 Wh/kg; or, charging ordischarging at a rate ≧4.5 A per g of storage compound, is greater than10 Wh/kg.

In another set of embodiments, an electrode comprising a lithium storagecompound is provided. The lithium storage compound is a compound otherthan one of ordered or partially ordered rocksalt crystal structuretype, or spinel crystal structure type, or vanadium oxide or manganeseoxide. The compound has a material energy density (i.e., voltage vs. Li×charge capacity) that while: charging or discharging at a rate ≧800 mAper g of storage compound, is greater than 250 Wh/kg; or, charging ordischarging at a rate ≧1.5 A per g of storage compound, is greater than180 Wh/kg; or, charging or discharging at a rate ≧3 A per g of storagecompound, is greater than 40 Wh/kg; or, charging or discharging at arate ≧4.5 A per g of storage compound, is greater than 10 Wh/kg.

In another set of embodiments, an electrode is provided. The electrodesincludes a current collector comprising any of the compounds describedabove.

In another set of embodiments, a storage battery cell is provided. Thestorage battery comprises a positive electrode, a negative electrode anda separator positioned between the positive electrode and the negativeelectrode. At least one of the positive electrode or negative electrodecomprises any of the compounds described above.

Other embodiments and novel features of the invention should becomeapparent from the following detailed description when considered inconjunction with the accompanying drawings. In cases of conflict betweenan incorporated reference and the present specification, the presentspecification shall control.

BRIEF DESCRIPTION OF DRAWINGS

Preferred, non-limiting embodiments of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 is a copy of an TEM image of a compound with 0.1% Ti doping,prepared according to the method substantially described in Example 1and heat treated at 600° C. in argon for twenty-four hours, showing thatthe primary crystallite size is about 100-200 nm and that the primarycrystallites are aggregated into larger particles; and showing thatthere is no surface coating or other continuous phase which couldprovide improved electronic conductivity; thus, the improved electronicconductivity is likely due to an improvement in the compound itself;

FIG. 2 are copies of scanning transmission electron microscope imagesand energy-dispersive x-ray composition maps of a 1% Ti-doped sampleprepared according to the method substantially described in Example 1and heat treated at 600° C. in nitrogen for twenty-four hours or 800° C.in argon for sixteen hours. In the sample heat treated at 600° C., thereis detectable Ti in solid solution in the compound as well as an excessof Ti appearing as an additional phase whereas the sample heat treatedat 800° C. shows no Ti detectable in the phase itself, thus showing thatthe solid solubility of Ti under these conditions is likely less thanabout 0.1%;

FIG. 3 are copies of scanning transmission electron microscope imagesand energy-dispersive x-ray composition maps of an 0.2% Nb-doped sampleprepared according to the method substantially described in Example 1and heat treated at 600° C. for twenty-four hours, 700° C. for twentyhours, and 800° C. for fifteen hours, all in argon, showing that in thesample heat treated at 600° C., substantial amounts of Nb can bedetected within the LiFePO₄ grains and a Nb-rich additional phase issubstantially absent; in the samples heat treated at 700° C. and 800°C., substantially less Nb is detectable in the grains and Nb-richadditional phase has appeared, and thus showing that the solubility ofNb is at least about 0.2% when the material is prepared according toExample 1 and heat treated at 600° C., whereas heat treating at atemperature of 700° C., or greater, causes exsolution of Nb;

FIG. 4 is a graph showing x-ray diffraction patterns of materialsprepared according to Example 1, undoped samples and samples containing1% Ti, 1% Zr, 2% Ti, and 2% Zr, heat treated at 600° C. in nitrogen fortwenty-four hours, showing that additional phases can be detectable inall of the doped samples and thus that, the solubility limit of thedopants is less than 1% under these preparation conditions; thecomposition heat treated in argon and nitrogen being substantiallysimilar to that shown in FIG. 15; thus showing that multiplenon-oxidizing gas atmospheres can be used to prepare the electronicallyconductive materials of the invention;

FIG. 5 is a copy of TEM images of a powder of nominal compositionLiFe_(0.99)Zr_(0.01)PO₄ and prepared according to the Example 1, showingcrystalline particles in which lattice fringes are visible and which donot possess a distinguishable surface phase of another material such ascarbon;

FIGS. 6A and 6B show X-ray diffraction patterns of various powdersshowing the effect of cation stoichiometry on dopant solid-solubility.FIG. 35A shows powders containing 1 atom % dopant in the stoichiometryLi_(1−x)M_(x)FePO₄ are single-phase by XRD and TEM/STEM analysis. FIG.35B shows powders containing 1 atom % dopant in the stoichiometryLiFe_(1−x)M_(x)PO₄ show Li₃PO₄ precipitation by XRD, and secondaryphases enriched in the dopant by TEM/STEM (not shown);

FIGS. 7A-7D show elemental maps obtained by STEM of a powder ofcomposition Li_(0.99)Nb_(0.01)FePO₄ (fired 600° C., 20 h, in argon)which illustrate the uniform dopant solid solution observed incompositions of stoichiometry Li_(1−x)M_(x)FePO₄;

FIGS. 8 and 9 are graphs showing the conductivity of doped and undopedsamples as a function of temperature;

FIG. 10 shows backscattered electron images of the polishedcross-section of two Nb-doped and one undoped pellet sintered to highdensity;

FIG. 11 is the configuration of a four-point microcontact measurementperformed to determine the electronic conductivity of samples;

FIG. 12 is the electrical conductivity measured at several locationswithin each of the three samples of FIG. 10;

FIG. 13 shows bright-field TEM images of powders of 1% Nb and 1% Zrdoping level and prepared according to the invention;

FIG. 14 shows a TEM image of a conductive 1% Nb doped composition firedat 600° C., showing a particle of incompletely reacted precursor andcrystallized olivine phase, and energy-dispersive X-ray spectra takenwith a focused electron probe at the locations indicated, showing thatcarbon is enriched within the particle of unreacted precursor and notdetected within several locations of the olivine phase;

FIGS. 15 and 16 show high resolution TEM images of a conductive 1% Nbdoped composition fired at 600 C, in which lattice fringes are visiblein crystallites of olivine phase, and showing the absence of asignificant surface coating of another material;

FIG. 17A shows a first electrochemical cycle for an electrode preparedusing a Nb-doped composition, and tested against a lithium metalnegative electrode in a laboratory cell using a nonaqueous liquidelectrolyte. FIG. 17B shows capacity vs. cycle number for this electrodeat a 1 C rate (150 mA/g). FIG. 17C shows the coulombic efficiency vs.cycle number at 1 C rate (150 mA/g);

FIGS. 18A and 18B show electrochemical test data for electronicallyconductive olivine of composition Li_(0.99)Zr_(0.01)FePO₄ s in aconventional lithium battery electrode design (78 wt % cathode-activematerial, 10 wt % Super P™ carbon, 12 wt % PVdF binder; 2.5 mg/cm²loading) with a lithium metal negative electrode and nonaqueous liquidelectrolyte. FIG. 18A shows results of cycle testing which indicateshigh and stable reversible capacity for more than 150 cycles at avariety of current rates. Significant capacity with high coulombicefficiency (>99.5%) is retained at rates as high as 3225 mA/g (21.5 C).FIG. 18B shows charge-discharge curves indicating little polarizationeven at the highest current rates, attributed to the high electronicconductivity and high specific surface area of the olivine powder;

FIG. 19 shows discharge curves for continuous cycling between 2-4.2V foran electrode made using Li_(0.99)Zr_(0.01)FePO₄ powder and tested todischarge rates of 66.2 C (9.93 A/g) at a temperature of 42° C. in aconventional cell design using a lithium metal negative electrode andnonaqueous liquid electrolyte;

FIG. 20 shows discharge curves for constant-current constant-voltagecycling between 2-3.8V for an electrode made usingLi_(0.99)Zr_(0.01)FePO₄ powder and tested to discharge rates of 200 C(30 A/g) at a temperature of 22° C. in a conventional cell design usinga lithium metal negative electrode and nonaqueous liquid electrolyte;

FIG. 21 shows discharge capacity vs. discharge rate curves for severalelectrodes formulated using Li_(0.99)Zr_(0.01)FePO₄ powder heat treatedat 600° C. or 700° C., and tested to high discharge rates greater than60 C (9 A/g) at 22-23° C. in a conventional cell design using a lithiummetal negative electrode and nonaqueous liquid electrolyte;

FIG. 22 shows discharge capacity vs. discharge rate curves for twoelectrodes formulated using undoped LiFePO₄ powder heat treated at 700°C., and tested at 23° C. in a conventional cell design using a lithiummetal negative electrode and nonaqueous liquid electrolyte;

FIG. 23 shows discharge capacity vs. discharge rate curves for severalLiFePO4 electrodes described in published literature, compared to anelectrode of the invention containing Li_(0.99)Zr_(0.01)FePO₄ powder,showing the markedly higher discharge capacity available at highdischarge rates of the electrodes of the invention;

FIG. 24 shows the discharge energy density in mAh/g vs. the currentdensity in mA/g for an electrode formulated usingLi_(0.99)Zr_(0.01)FePO₄ powder and measured at a temperature of 22° C.;

FIG. 25 shows the discharge energy density in mAh/g vs. the currentdensity in mA/g for an electrode formulated usingLi_(0.99)Zr_(0.01)FePO₄ powder and measured at temperatures of 23, 31,and 42° C.;

FIG. 26 shows the discharge energy density in mAh/g vs. the currentdensity in mA/g for an electrode formulated usingLi(Fe_(0.98)Ti_(0.02))PO₄ powder and measured at 23° C.;

FIG. 27 shows the discharge energy density in mAh/g vs. the currentdensity in mA/g for an electrode formulated using undoped LiFePO4 andmeasured at temperatures of 23, 31, and 42° C.

FIG. 28 shows a Ragone plot of log power density vs. log energy densityfor storage battery cells based on the lithium storage materials andelectrodes of the invention, compared with other storage batterytechnology, showing the improved power density that is available whilestill having high energy density.

FIG. 29 shows a schematic storage battery cell according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

LiFePO₄ and Li(Mn,Fe)PO₄ are ordered olivine structure compounds alsoknown as the mineral triphylite. They belong to the general group knownas polyanion compounds with tetrahedral “anion” structural units(XO₄)^(n−), along with oxygen octahedra occupied by a transition metalM, and can include compounds of Li_(x)MXO₄ (olivine), Li_(x)M₂(XO₄)₃(NASICON), VOPO₄, LiFe(P₂O₇) or Fe₄(P₂O₇)₃ structure, and structuresrelated to these by having additional metal ions occupying interstitialsites, symmetry-changing displacements, or minor changes in theconnectivity of polyhedra. Here, X is comprised of a metal that canoccupy tetrahedral sites within the polyanion groups and has asignificant covalent bonding character. X can be P, S, As, Mo, W, Al,Si, or B. According to the present invention, these compounds can beused as lithium storage electrode materials because of their highlithium-insertion potential (relative to lithium metal), hightheoretical capacity, low cost, ease of synthesis, and stability whenused with common organic electrolyte systems. Despite thesecharacteristics, it has been widely recognized that one of thelimitations of this series of compounds is their low electronicconductivity, which greatly limits the practicality of these materialsin battery systems. Related compounds such as (Mg,Fe)SiO₄ are alsoelectronic insulators at an near room temperature, and only haveappreciable electronic conductivity at greatly elevated temperatures.

It is therefore a surprising and unexpected discovery that certaincompositions of LiFePO₄, prepared from starting materials of lithiumsalts, iron compounds, and phosphorous salts, including but not limitedto, lithium carbonate, ammonium phosphate, and iron oxalate, and towhich a low additional concentration of a metal supervalent to Li, suchas, but not limited to, Mg, Al, Ti, Fe, Mn, Zr, Nb, Ta, and W, such asin the form of a metal oxide or metal alkoxide, have been added, andwhich is heat treated (HT) at a certain temperature range andatmosphere, exhibit increased electronic conductivity at and near roomtemperature to render the compounds useful as lithium storage materials.

As used herein, the electrical conductivity of materials will be givenin units of S/cm, electrical resistivity in units of ohm-cm (Ω-cm),resistance in ohms (Ω), charge and discharge capacity in units of amperehours per kilogram of the storage material (Ah/kg) or milliampere hourper gram of storage material (mAh/g), charge and discharge rate in unitsof both milliamperes per gram of the storage compound (mA/g), and Crate. When given in units of C rate, the C rate is defined as theinverse of the time, in hours, necessary to utilize the full capacity ofthe battery measured at a slow rate. A rate of 1 C refers to a time ofone hour; a rate of 2 C refers to a time of half an hour, a rate of C/2refers to a time of two hours, and so forth. Typically, the C rate iscomputed from the rate, in mA/g, relative to the capacity of thecompound or battery measured at a lower rate of C/5 or less. Forexample, in some examples herein the nominal capacity of a doped LiFePO₄compound at low rate is about 150 mAh/g, and therefore a rate of 1 Ccorresponds to a current rate of 150 mA/g, a rate of C/5 corresponds to30 mA/g, a rate of 5 C corresponds to 750 mA/g, and so forth.

In one aspect, the present invention is directed to increasing theelectronic conductivity of transition metal polyanion compounds so thatthey can be used as alkali ion storage materials, for example,rechargeable lithium ion batteries. The compounds of the invention haveelectronic conductivities near room temperature, for example at atemperature of 22° C.-27° C., of at least about 10⁻⁸ S/cm. However, insome cases, the conductivity is at least about at least about 10⁻⁷ S/cm,in other cases, at least about 10⁻⁶ S/cm, in yet other cases, at leastabout 10⁻⁵ S/cm, in still other cases, at least about 10⁻⁴ S/cm, inpreferred cases, at least about 10⁻³ S/cm, and in more preferred cases,at least about 10⁻² S/cm. Where elements and groups in the PeriodicTable are referred to, the Periodic Table catalog number S-18806,published by the Sargent-Welch company in 1994, is used as a reference.

In one aspect, the present invention is directed to increasing theelectronic conductivity of transition metal polyanion compounds so thatthey can be used as alkali ion storage materials, for example,rechargeable lithium ion batteries, without adding excessive amounts ofan additional conductive compound such as carbon. Accordingly, thepresent invention can include conductivity-enhancing additives, such asbut not limited to conductive carbon black, at, for example, less thanabout 15 weight percent, or in some cases, less than about 10 weightpercent, in other cases, less than about 7 weight percent, in othercases, less than 3 weight percent, in other cases, less than 1 weightpercent and, in some cases, no conductivity-enhancing additive.

In another aspect, the present invention is directed to decreasing theparticle or crystallite size, or increasing the specific surface area(typically given in square meters per gram of the material, m²/g, andmeasured by such methods as the Brunauer-Emmett-Teller (BET) gasadsorption method) of transition metal polyanion compounds in order toprovide improved electrochemical energy storage, including improvedcharge storage capacity, improved energy density and power density whenused in an electrochemical cell, and improved cycle life when theelectrochemical cell is reversibly charged and discharged. Compositionsare provided for compounds of high specific surface area, includingthose that are substantially fully crystallized, or those that havesubstantial electronic conductivity. The materials of the invention havespecific surface areas of at least 15 m²/g. However, in other cases theyhave specific surface areas of at least 20 m²/g, in other cases at least30 m²/g, and in other cases at least 40 m²/g.

In another aspect, the present invention provides methods for preparingthe transition metal polyanion compounds of the invention, includingcompounds with substantial electronic conductivity and/or high specificsurface area and small particle or crystallite size.

In another aspect, the invention comprises storage electrodes, includingthose using the transition metal polyanion compounds of the invention.Such storage electrodes have useful properties for electrochemicalenergy storage including having high storage energy density, high powerdensity, and long cycle life when used reversibly in an electrochemicaldevice. Formulations of and methods for preparing said electrodes areprovided.

In another aspect, the invention comprises storage battery cells,including those using the transition metal polyanion compounds of theinvention. Such cells have useful energy storage characteristicsincluding high energy density and high power density, and long cyclelife.

Electronic Conductivity

In one embodiment, the present invention provides an electrochemicaldevice comprising an electrode comprising a compound with a formulaLi_(x)Fe_(1−a)M″_(a)PO₄, and a conductivity at 27° C., of at least about10⁻⁸ S/cm. However, in some cases, the conductivity is at least about atleast about 10⁻⁷ S/cm, in other cases, at least about 10⁻⁶ S/cm, in yetother cases, at least about 10⁻⁵ S/cm, in still other cases, at leastabout 10⁻⁴ S/cm, in preferred cases, at least about 10⁻³ S/cm, and inmore preferred cases, at least about 10⁻² S/cm.

In another embodiment, the present invention provides an electrochemicaldevice comprising an electrode comprising a compound with a formulaLi_(x)Fe_(1−a)M″_(a)PO₄, the compound having a gravimetric capacity ofat least about 80 mAh/g while the device is charging/discharging atgreater than about C rate. However, in some embodiments, the capacity isat least about 100 mAh/g, or in other embodiments, at least about 120mAh/g, in preferred embodiments, at least about 150 mAh/g, and in stillother embodiments, at least about 160 mAh/g. The present invention can,in some embodiments, also provide a capacity up to the theoreticalgravimetric capacity of the compound.

In another embodiment, the present invention provides an electrochemicaldevice comprising an electrode comprising a compound with a formulaLi_(x−a)M″_(a)FePO₄.

In another embodiment, the present invention provides an electrochemicaldevice comprising an electrode comprising a compound with a formulaLi_(x−a)M″_(a)FePO₄, and a conductivity at 27° C. of at least about 10⁻⁸S/cm. However, in some cases, the conductivity is at least about atleast about 10⁻⁷ S/cm, in other cases, at least about 10⁻⁶ S/cm, in yetother cases, at least about 10⁻⁵ S/cm, in still other cases, at leastabout 10⁻⁴ S/cm, and in preferred cases, at least about 10⁻³ S/cm, andin more preferred cases, at least about 10⁻² S/cm.

In another embodiment, the present invention provides an electrochemicaldevice comprising an electrode comprising a compound with a formulaLi_(x−a)M″_(a)FePO₄, the compound having a gravimetric capacity of atleast about 80 mAh/g while the device is charging/discharging at greaterthan about C rate. However, in some embodiments, the capacity is atleast about 100 mAh/g, or in other embodiments, at least about 120mAh/g, in preferred embodiments, at least about 150 mAh/g and in stillother preferred embodiments, at least about 170 mAh/g. The presentinvention can, in some embodiments, also provide a capacity up to thetheoretical gravimetric capacity of the compound.

According to one embodiment, a composition comprising a compound with aformula A_(x)(M′_(1−a)M″_(a))_(y)(XD₄)_(z),A_(x)(M′_(1−a)M″_(a))_(y)(DXD₄)_(z), orA_(x)(M′_(1−a)M″_(a))_(y)(X₂D₇)_(z), has a conductivity at about 27° C.of at least about 10⁻⁸ S/cm, wherein A is at least one of an alkalimetal and hydrogen, M′ is a first-row transition metal, X is at leastone of phosphorus, sulfur, arsenic, molybdenum and tungsten, M″ is anyof a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB,and VIB metal, D is at least one of oxygen, nitrogen, carbon, or ahalogen, 0.0001<a≦0.1, and x, y, and z have values such that x plus thequantity y(1−a) times a formal valence or valences of M′, plus thequantity ya times a formal valence or valence of M″, is equal to z timesa formal valence of the XD₄, X₂D₇, or DXD₄ group. x, y, and z aretypically greater than 0. The conductivity of the compound can be atleast about 10⁻⁵ S/cm, at least about 10⁻⁴ S/cm, and, in some cases, atleast about 10⁻² S/cm. In some embodiments, A is lithium and x/(x+y+z)can range from about zero to about one third, or about zero to about twothirds. In one embodiment, X is phosphorus, while in other embodiments,M′ is iron. M″ can be any of aluminum, titanium, zirconium, niobium,tantalum, tungsten, or magnesium. M″ can be substantially in solidsolution in the crystal structure of the compound. Typically, thecompound has at least one of an olivine, NASICON, VOPO₄, LiFe(P₂O₇) orFe₄(P₂O₇)₃ structure, or mixtures thereof.

In some embodiments, the compound is LiFePO₄.

In some embodiments, M″ is at least partially in solid solution in thecrystal structure of the compound at a concentration of at least 0.01mole % relative to the concentration of M′, the balance appearing as anadditional phase, at least 0.02 mole % relative to the concentration ofM′, the balance appearing as an additional phase, and in yet otherembodiments, at least 0.05 mole % relative to the concentration of M′,the balance appearing as an additional phase and, in still otherembodiments, at a concentration of at least 0.1 mole % relative to theconcentration of M′, the balance appearing as an additional phase.

In some embodiments, the compound can be formed as particles orcrystallites wherein at least 50% of which have a smallest dimensionthat is less than about 500 nm. However, in some cases, the smallestdimension is less than 200 nm, in yet other cases, the smallestdimension is less than 100 nm, in still other cases, the smallestdimension is less than 50 nm, in still other cases, the smallestdimension is less than 20 nm, and in still other cases, the smallestdimension is less than 10 nm. In some embodiments, the compound forms aninterconnected porous network comprising crystallites with a specificsurface area of at least about 10 m²/g. However, in some cases, thespecific surface area is at least about 20 m²/g, in other cases, thespecific surface area is at least about 30 m²/g, in other cases, thespecific surface area is at least about 40 m²/g, in other cases, thespecific surface area is at least about 50 m²/g. Smallest dimension, inthis context, means a cross-section.

In some cases, the present invention provides a compound with a formula(A_(1−a)M″_(a))_(x)M′_(y)(XD₄)_(z), (A_(1−a)M″_(a))_(x)M′_(y)(DXD₄)_(z),or (A_(1−a)M″_(a))_(x)M′_(y)(X₂D₇)_(z) that has a conductivity at 27° C.of at least about 10⁻⁸ S/cm, wherein A is at least one of an alkalimetal and hydrogen, M′ is a first-row transition metal, X is at leastone of phosphorus, sulfur, arsenic, molybdenum, and tungsten, M″ any ofa Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB,and VIB metal, D is at least one of oxygen, nitrogen, carbon, or ahalogen, 0.0002<a≦0.1, and x, y, and z have values such that (1−a)_(x)plus the quantity ax times the formal valence or valences of M″ plus ytimes the formal valence or valences of M′ is equal to z times theformal valence of the XD₄, X₂D₇ or DXD₄ group. x, y, and z are typicallygreater than zero. The conductivity of the compound can be at leastabout 10⁻⁵ S/cm, at least about 10⁻⁴ S/cm, and, in some cases, at leastabout 10⁻² S/cm. In some embodiments, A is lithium and x/(x+y+z) canrange from about zero to about one third. In one embodiment, X isphosphorus, while in other embodiments, M′ is iron. M″ can be any ofaluminum, titanium, zirconium, niobium, tantalum, tungsten, ormagnesium. M″ can be substantially in solid solution in the crystalstructure of the compound. Typically, the compound has at least one ofan olivine, NASICON, VOPO₄, LiFe(P₂O₇) or Fe₄(P₂O₇)₃ structure, ormixtures thereof. In some embodiments, the compound is LiFePO₄. In someembodiments, M″ is at least partially in solid solution in the crystalstructure of the compound at a concentration of at least 0.01 mole %relative to the concentration of M′, the balance appearing as anadditional phase, at least 0.02 mole % relative to the concentration ofM′, the balance appearing as an additional phase, and in yet otherembodiments, at least 0.05 mole % relative to the concentration of M′,the balance appearing as an additional phase and, in still otherembodiments, at a concentration of at least 0.1 mole % relative to theconcentration of M′, the balance appearing as an additional phase.

In some embodiments, the electronically conductive lithium transitionmetal phosphate olivine compound has a suitable electronic conductivitygreater than about 10⁻⁸ S/cm. The electronically conductive lithiumtransition metal phosphate compound can be a compositionLi_(x)(M′_(1−a)M″_(a))PO₄ or Li_(x−a)M″_(a)M′PO₄, and can crystallize inthe ordered-olivine or triphylite structure, or a structure related tothe ordered olivine or triphylite structure with small displacements ofatoms without substantial changes in the coordination number of anionsaround cations, or cations around anions. In such compounds Li⁺substantially occupies the octahedral site typically designated as M1,and a substantially divalent cation M′ substantially occupies theoctahedrally-coordinated site typically designated as M2, as describedin the olivine structure given in “Crystal Chemistry of SilicateMinerals of Geophysical Interest,” by J. J. Papike and M. Cameron,Reviews of Geophysics and Space Physics, Vol. 14, No. 1, pages 37-80,1976. In some embodiments, the exchange of Li and the metal M′ betweentheir respective sites in a perfectly ordered olivine structure isallowed so that M′ may occupy either site. M′ is typically one or moreof the first-row transition metals, V, Cr, Mn, Fe, Co, or Ni. M″ istypically a metal with formal valence greater than 1+ as an ion in thecrystal structure.

In some embodiments, M′, M″, x, and a are selected such that thecompound is a crystalline compound that has in solid solution chargecompensating vacancy defects to preserve overall charge neutrality inthe compound. In the compositions of type Li_(x)(M′_(1−a)M″_(a))PO₄ orLi_(x−a)M″_(a)M′PO₄, this condition can be achieved when a times theformal valence of M″ plus (1−a) times the formal valence of M′ plus x isgreater than 3+, necessitating an additional cation deficiency tomaintain charge neutrality, such that the crystal composition isLi_(x)(M′_(1−a−y)M″_(a)vac_(y))PO₄ or Li_(x−a)M″_(a)M′_(1−y)vac_(y)PO₄,where vac is a vacancy. In the language of defect chemistry, the dopantcan be supervalent and can be added under conditions of temperature andoxygen activity that promote ionic compensation of the donor, resultingin nonstoichiometry. The vacancies can occupy either M1 or M2 sites.When x<1, the compound also has additional cation vacancies on the M1site in a crystalline solid solution, said vacancies being compensatedby increasing the oxidation state of M″ or M′. In order to increase theelectronic conductivity usefully, a suitable concentration of saidcation vacancies should be greater than or equal to 10¹⁸ per cubiccentimeter.

In some cases, the compound has an olivine structure and contains incrystalline solid solution, amongst the metals M′ and M″, simultaneouslythe metal ions Fe²⁺ and Fe³⁺, Mn²⁺ and Mn³⁺, Co²⁺ and Co³⁺, Ni²⁺ andNi³⁺, V²⁺ and V³⁺, or Cr²⁺ and Cr³⁺, with the ion of lesserconcentration being at least 10 parts per million of the sum of the twoion concentrations.

In some embodiments, the compound has an ordered olivine structure andA, M′, M″, x, and a are selected such that there can be Li substitutedonto M2 sites as an acceptor defect. In the compositions of typeLi_(x)(M′_(1−a)M″_(a))PO₄ or Li_(x−a)M″_(a)M′PO₄, typical correspondingcrystal compositions are Li_(x)(M′_(1−a−y)M″_(a)Li_(y))PO₄ orLi_(x−a)M″_(a)M′_(1−y)Li_(y)PO₄. In this instance, the subvalent Lisubstituted onto M2 sites for M′ or M″ can act as an acceptor defect. Inorder to increase the electronic conductivity usefully, a suitableconcentration of said Li on M2 sites should be greater than or equal to10¹⁸ per cubic centimeter.

In some embodiments, the present invention provides a p-typesemiconducting composition, Li_(x)(M′_(1−a)M″_(a))PO₄,Li_(x)M″_(a)M′PO₄, Li_(x)(M′_(1−a−y)M″_(a)vac_(y))PO₄,Li_(x−a)M″_(a)M′_(1−y)vac_(y)PO₄, Li_(x)(M′_(1−a−y)M″_(a)Li_(y))PO₄ orLi_(x−a)M″_(a)M′_(1−y)Li_(y)PO₄. M″ is a Group IIA, IIIA, IVA, VA, VIA,VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB element of the PeriodicTable (catalog number S-18806, published by the Sargent-Welch company in1994.) Magnesium is an example of a dopant from Group IIA, Y is anexample of a dopant from Group IIIA, Ti and Zr are examples of dopantsfrom Group IVA, Nb and Ta are examples of dopants from Group VA, W is anexample of a dopant from Group VIA, Fe is an example of a metal fromGroup VIIIA, and Al is an example of a dopant from Group IIIB.

x can have a value between zero and 1.1 in the initially preparedmaterial, and during its use as an lithium ion storage compound, x canvary between about zero and about 1.1. a can have a value between about0.0001 and 0.1. In some embodiments, out of the total amount a of M″, atleast 0.0001 is in solid solution in the crystalline structure of thecompound.

In some embodiments, M′ is Fe and the solubility of M″ in the latticecan be improved if M″ has an ionic radius, in octahedral coordination,that is less than that of Fe²⁺. Achieving solid solubility sufficient toincrease the electronic conductivity above 10⁻⁸ S/cm can require thatprocessing conditions (for example, temperature, atmosphere, startingmaterials) allow M″ to be stabilized in a particular valence state thatwould provide an ionic radius less than that of Fe²⁺. In some cases, forexample, when solid solubility is achieved, the M″ ion may occupy the M1site, or it may preferentially occupy the M2 site and cause Fe²⁺ orFe³⁺, which would normally occupy the M2 site, to occupy the M1 site.

Generalizing the M″ solubility requirement to other olivines ofcomposition Li_(x−a)M″_(a)M′PO₄, M″ typically has an ionic radius thatis less than the average ionic radius of ions M′ at the Li concentrationx at which the compound is first synthesized. Electrochemical insertionand removal can later change the valence distribution amongst the M′ andM″ ions.

In some cases, M″ can be in the desired valence state and concentrationby adding, to the starting material, a salt of M″ having the desiredfinal valence. However, the desired valence distribution amongst metalsM′ and M″ can be obtained by synthesizing or heat treating underappropriate conditions of temperature and gas atmosphere. For example,if M′ is Fe, heat treatment should be conducted under temperature andatmosphere conditions that preserve a predominantly 2+ valence state,although some Fe³⁺ is allowable and can even be beneficial forincreasing conductivity.

In other cases, for example, for Li_(x)(M′_(1−a)M″_(a))PO₄ compositions,firing or heat treating at 600° C., can render the compositionsconductive, even if M″, or M′, is a divalent cation, such as Mg²⁺ orMn²⁺. In some cases, a Li₃PO₄ secondary phase can be present. Thus, theolivine composition according to some embodiments of the presentinvention may have a lithium deficiency that can result in aLi_(x−a)M″_(a)M′PO₄ crystal composition.

The possible dopants M″ are not limited to those Groups of the PeriodicTable that were previously identified, rather, M″ can be any metal thatsatisfies the above requirements of size and valence. Specifically, forcompositions Lixa M′_(a)M″PO₄, where M′ is Fe, M″ may be Mg²⁺, Mn²⁺,Fe³⁺, Al³⁺, Ce³⁺, Ti⁴⁺, Zr⁴⁺, Hf⁴⁺, Nb⁵⁺, Ta⁵⁺, W⁴⁺, W⁶⁺, orcombinations thereof.

In another embodiment, the compounds of this invention can be used asmixed protonic-electronic conductors for such applications as fuel cellelectrodes and gas-separation membranes. Phospho-olivines, such asLiFePO₄, can be doped to be highly electronically conducting, while atthe same time they can be sufficiently lithium-ion conducting to providegood performance as a lithium battery electrode. Electrochemical resultsshow good cycling and also demonstrate that the compound can bedelithiated while retaining good electronic conductivity. In some cases,the olivine structure can be retained in the fully delithiated state.That is, FePO₄ has an olivine structure-type polymorph. Therefore, adoped FePO₄ may be protonatable to be a good mixed protonic-electronicconductor, since phosphates are good protonic conductors.

The conductive LiMPO₄ compounds of this invention may also beprotonatable to form H_(x)FePO₄ conductors, where 0<x<1.1. Suchcompounds can be used as the electrode in a proton-conducting fuel cell.Typically such an electrode can be used with a proton-conducting andelectronically insulating electrolyte. Such compounds can also be usedas a solid membrane for separating hydrogen gas from gas mixtures. Forexample, hydrogen can be dissociated to protons and electrons at onesurface of the membrane that is under a higher hydrogen partialpressure, the protons would typically diffuse through the membrane to asecond surface at lower hydrogen partial pressure, and are recombinedwith electrons to form hydrogen gas that would be released to theatmosphere from the second surface.

In some embodiments, compounds of the invention have a structurecomprising a continuous network of transition-metal filled anionpolyhedral units. The polyhedral units may be octahedrals or distortedoctahedrals. The polyhedral units in the structure can, for example,share at least one of vertices, corners, edges, or faces with otherpolyhedral units. In some cases, the polyhedral units share corners andedges with other polyhedral units.

In some embodiments, the compound is an n-type conductor. In others, thecompound is a mixture of an n-type conductor and a p-type conductor. Instill others, the compound is a p-type conductor.

In some embodiments, the compound is substantially fully delithiated.The compound may be a p-type conductor when substantially fullylithiated and an n-type conductor when substantially fully delithiated.In some cases, the compound, upon delithiation, undergoesphase-separation into a substantially lithiated compound and asubstantially delithiated compound, each of which have an electronicconductivity of at least 10⁻⁶ S/cm.

The compounds of the present invention can be prepared through a varietyof techniques, including, for example, solid-state reactions,co-precipitation from liquid solutions, so-called sol-gel methods, ordeposition from the vapor phase by methods such as sputtering, laserablation, electron-beam evaporation, thermal evaporation, and chemicalvapor deposition. For large volume production, for example, suchcompositions can be prepared by solid state reaction methods. For suchreactions, numerous possible starting materials are possible, the use ofwhich allows a general classification of the methods.

Salts of each of the metals are typically selected so that they canreact and decompose upon heating. Examples include salts such asNH₄H₂PO₄, Li₂CO₃, and FeC₂O₄.2H₂O for the main constituents (when, forexample, M″ is Fe), and an alkoxide or metallorganic compound such asZr(OC₂H₄)₄, Ti(OCH₃)₄(CH₃OH)₂, Nb(OC₆H₅)₅, Ta(OCH₃)₅, W(OC₂H₅)₆,Al(OC₂H₅)₃, or Mg(OC₂H₅)₂ as the source of the metal M″. When using oneor more of these materials as the starting materials, gaseous speciessuch as carbon oxides, hydrogen, water, and ammonia can be generated andremoved, if necessary, during preparation.

The oxide Li₂O, a divalent oxide of the metal M″ (such as FeO, MnO, orCoO), and P₂O₅ can be used as the source of the main constituents. Themetal M″ is typically added as its oxide in the preferred valence state,for example, as MgO, TiO₂, ZrO₂, Fe₂O₃, Nb₂O₅, Ta₂O₅, Al₂O₃, WO₃, orWO₆. When using such exemplary starting materials, the compound can becrystallized with substantially little or no evolution, or introduction,of gaseous species. That is, the reaction of the starting can beconducted in a closed-reaction system, typically without substantialmass transport in, or out.

The present invention allows any mixture of starting materials, some ofwhich will yield a decomposition product, and some of which will not.For example, a portion of the starting materials can react to evolve orabsorb gaseous species during formation thereof. If Li₂CO₃ or LiOH.nH₂Ois used as the lithium source, carbon oxide, or water, or both can begenerated during formation. Other constituents of the compound aretypically provided as oxide thereof, typically in the preferred formalvalence, (for example, as FeO, P₂O₅, and Nb₂O₅), which typically do notevolve or absorb gaseous species during the reaction. In otherinstances, starting materials may be used that substantially comprise aclosed system in which there is little or no mass transport in or out ofthe reactants during formation of the materials of the invention. Onepreferred such reaction uses LiPO₃ and FeO to form LiFePO₄ as theproduct. Adjustments to the relative amounts of the reactants, and theaddition of other constituents such as the dopants in the form of oxidesin which the cations have their preferred formal valence state, arereadily used in order to obtain compositions comprising the materials ofthe invention.

The dopants M″ can also be added by milling the starting materials inmilling media comprising the desired doping materials. For example,zirconia or alumina milling balls or cylinders can be used to introduceZr or Al as the dopant. Milling equipment, such as a milling container,made of such materials can also be used as the source of dopant. Theamount of dopant can be controlled by monitoring the extent, intensityor duration or both, of milling and controlling such until apredetermined dopant level is achieved.

Further, milling media or containers can be used to add carbon, forexample, to the materials of the invention in small quantities that canhave a beneficial effect on the conductivity of the material withoutsubstantially decreasing the energy density of the material. The amountof carbon added in this instance is preferably less than about 10 weightpercent of the total mass of the material, more preferably less thanabout 5 weight percent, and still more preferably less than about 3weight percent. Milling containers or milling media that have sucheffect include those made from polypropylene, polyethylene, polystyrene,and fluoropolymers such as Teflon® (E.I du Pont de Nemours and Company,Wilmington, Del.).

For Li_(x)(M′_(1−a)M″_(a))PO₄ compositions, a is preferably less thanabout 0.05 and the compound is preferably heat treated under variousconditions.

A substantially reducing or inert gas atmosphere can be used, forexample, nitrogen, argon, nitrogen-hydrogen mixtures, carbondioxide-carbon monoxide mixtures, or mixtures of nitrogen with oxygen orargon with oxygen. The oxygen partial pressure in the gas mixture underthe firing conditions applied to the composition is typically less thanabout 10³ atm, preferably less than about 10⁻⁴ atm, more preferably lessthan about 10⁻⁵ atm, and still preferably less than about 10⁻⁶ atm. Whenusing salts that can decompose to yield gaseous products upon heating,the compounds can be exposed to a first heat treatment to decompose, insome cases, the salts leaving substantially only the oxides of eachmetal, at a lower temperature than the final crystallization heattreatment. For example, heat treatment at 350° C. for ten hours inflowing nitrogen or argon is typically sufficient to transform thestarting materials if the batch size is a few grams. A final heattreatment at a higher temperature typically follows. In some cases, thematerial is not heated to temperatures greater than about 800° C. forlonger than about four hours. Preferably, the material is heated at lessthan about 750° C. but greater than about 500° C., and is held at thattemperature between four and twenty-four hours.

For Li_(x−a)M″_(a)M′PO₄ compositions, a is preferably less than 0.1 andthe material can be heated to higher temperatures and for longer timesthan described above, without losing electronic conductivity. That is,these compositions can be subjected to much wider ranges of heattreatment temperature and time while still yielding high electronicconductivity. Various heat treatments can also be used. For example, asubstantially reducing or inert gas atmosphere is used, for example,nitrogen, argon, nitrogen-hydrogen mixtures, carbon dioxide-carbonmonoxide mixtures, or mixtures of nitrogen with oxygen or argon withoxygen. The oxygen partial pressure in the gas mixture under the firingconditions applied to the composition is typically less than about 10⁻⁴atmosphere, preferably less than about 10⁻⁵ atm, and still preferablyless than about 10⁻⁶ atm. When using salts that decompose to yieldgaseous products upon heating, the compounds may be exposed to a firstheat treatment to decompose, in some cases, the salts leavingsubstantially only the oxides of each metal, at a lower temperature thanthe final crystallization heat treatment. For example, a heat treatmentat 350° C. for ten hours in flowing nitrogen or argon can be sufficientto transform the starting materials if the batch size is a few grams. Afinal heat treatment at a higher temperature typically follows. In somecases, the material is heated to a temperature preferably greater than500° C. and less than about 900° C., still preferably greater than about550° C. and less than about 800° C., and is held at that temperaturebetween four and twenty-four hours.

While a detailed understanding of the conduction mechanism in thematerials of the present invention is not necessary to define or topractice the invention, it is useful to elaborate a possible mechanismthat is consistent with the experimental observations.

Measurements show that the highly conductive compositions are typicallyp-type, not necessarily n-type, while the undoped compositions can ben-type. This shows that acceptor defects can be introduced by doping andheat treating as described herein. Having a supervalent cation on the M1site can introduce a donor on that site. However, since the resultingmaterials are p-type, it is believed that electronic compensation of adonor cation is not necessarily the mechanism by which conductivityincreases. Having vacancies on the M2 iron sites, for ionic compensationof supervalent cations on the M1 sites, or in order to charge-compensatean excess of Fe³⁺ introduced on the M2 sites, can introduce acceptorstates on the M2 sites. This is analogous to having a subvalent dopanton the Fe site, and can create an acceptor defect on the M2 sites.Having lithium substituted for a cation of higher valence on the M2sites can also create acceptor defects on those sites. Having lithiumdeficiency on the M1 site can also create acceptor defects on thosesites.

Therefore, highly conductive p-type behavior can be obtained when thereare acceptor defects or ions on the M1 or M2 sites that are notsimultaneously charge-compensated by other solutes or defects. However,for increased p-type conductivity to be obtained in the compound, it ispreferred that such acceptor defects form a crystalline solid solutionof the compound. For instance, in the undoped and insulating compoundLiFePO₄, if upon delithiation to an overall composition Li_(x)FePO₄where x<1, the compound forms two compositions or phases, LiFePO₄ inwhich Fe is substantially all in the ferrous (2+) state, and FePO₄ inwhich Fe is substantially all in the ferric (3+) state, then eachindividual compound comprising the material is substantially insulating,resulting in a whole material that is also insulating.

Thus, in one embodiment, the present invention provides a compoundcomprising a composition with a formulaA_(x)(M′_(1−a)M″_(a))_(y)(XD₄)_(z), A_(x)(M′_(1−a)M″_(a))_(y)(DXD₄)_(z),or A_(x)(M′_(1−a)M″_(a))_(y)(X₂D₇)_(z), having a conductivity at 27° C.of at least about 10⁻⁸ S/cm. In some embodiments, A is at least one ofan alkali metal and hydrogen, M′ is a first-row transition metal, X isat least one of phosphorus, sulfur, arsenic, molybdenum and tungsten, M″is any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,IVB, VB, and VIB metal of the Periodic Table (catalog number S-18806,published by Sargent-Welch, 1994), D is at least one of oxygen,nitrogen, carbon, or a halogen, 0.0001<a≦0.1, and x, y, and z aregreater than 0 and have values such that x, plus y(1−a) times a formalvalence or valences of M′, plus ya times a formal valence or valence ofM″, is equal to z times a formal valence of the XD₄, X₂D₇, or DXD₄group. In another embodiment, the present invention provides a compoundcomprising a composition with a formula(A_(1−a)M″_(a))_(x)M′_(y)(XD₄)_(z), (A_(1−a)M″_(a))_(x)M′_(y)(DXD₄)_(z),or (A_(1−a)M″_(a))_(x)M′_(y)(X₂D₇)_(z), having a conductivity at 27° C.of at least about 10⁻⁸ S/cm. In some embodiments, A is at least one ofan alkali metal and hydrogen, M′ is a first-row transition metal, X isat least one of phosphorus, sulfur, arsenic, molybdenum and tungsten, M″is any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,IVB, VB, and VIB metal, 0.0001<a≦0.1, and x, y, and z are greater than 0and have values such that x, plus y(1−a) times a formal valence orvalences of M′, plus ya times a formal valence or valence of M″, isequal to z times a formal valence of the XD₄, X₂D₇, or DXD₄ group.

In yet another embodiment, the present invention provides a fuel cellcomprising a mixed proton conducting and electronically conductingmaterial having a formula A_(x)(M′_(1−a)M″_(a))_(y)(XD₄)_(z),A_(x)(M′_(1−a)M″_(a))_(y)(DXD₄)_(z),A_(x)(M′_(1−a)M″_(a))_(y)(X₂D₇)_(z), (A_(1−a)M″_(a))_(x)M′_(y)(XD₄)_(z),(A_(1−a)M″_(a))_(x)M′_(y)(DXD₄)_(z), or(A_(1−a)M″_(a))_(x)M′_(y)(X₂D₇)_(z). In the compound, A is at least oneof an alkali metal and hydrogen, M′ is a first-row transition metal, Xis at least one of phosphorus, sulfur, arsenic, molybdenum, andtungsten, M″ any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB,IIB, IIIB, IVB, VB, and VIB metal, D is at least one of oxygen,nitrogen, carbon, or a halogen, 0.0001<a≦0.1, and x, y, and z aregreater than 0 and have values such that x, plus y(1−a) times the formalvalence or valences of M′, plus ya times the formal valence or valencesof M″, is equal to z times the formal valence of the XD₄, X₂D₇ or DXD₄group.

In some embodiments of the invention, it may be preferable for thecompound to be substantially free of silicon. That is, silicon is notpresent in amounts greater than trace amounts.

In a further embodiment, the present invention provides a compositionhaving a conductivity at about 27° C. of at least about 10⁻⁸ S/cmcomprising primary crystallites with a formula LiFePO₄. The primarycrystallites having an olivine structure that can form at least a partof an interconnected porous network.

In still another embodiment, the present invention provides a method ofproviding electrical energy. The method comprises the step of providinga battery having an electrode comprising a compound having aconductivity at 27° C. of at least about 10⁻⁸ S/cm and a capacity of atleast about 80 mAh/g. The method further comprises the step of chargingthe battery at a rate that is greater than about C rate of the compound.

In still another embodiment, the present invention provides a method offorming a compound. The methods include mixing an alkali metal orhydrogen salt, a first-row transition metal salt, a salt of at least oneof phosphorus, sulfur, arsenic, silicon, aluminum, boron, vanadium,molybdenum and tungsten, and a salt of any of a Group IIA, IIIA, IVA,VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal. The methodfurther includes milling the mixture and heat treating the mixture at atemperature between 300-900° C. This method may be used to form anysuitable compound described herein.

In yet another embodiment, the present invention is directed to a methodof doping a material to form a conductive material. The method comprisesthe steps of mixing powders of a lithium salt and an iron oxide andadding an oxide of a dopant, the dopant having the same valence state inthe oxide as in the conductive material. The method also comprises thestep of heat treating the mixed powders to form the doped conductivematerial.

And, in one embodiment, the present invention is directed to a method ofdoping a material to form a conductive compound. The method comprisesthe steps of selecting a starting material to be doped, in conjunctionwith selection of milling equipment comprising a dopant for doping thestarting material at a predetermined level of dopant and milling thestarting material in the milling equipment. The method further comprisesthe step of recovering from the milling step a material suitable forforming a conductive material comprising the starting material dopedwith the dopant at the predetermined level.

Amongst other applications, the compounds, electrodes, and battery cellsof the invention are useful for high power, safe, rechargeable lithiumbatteries for applications such as hybrid and electric vehicles, back-uppower, implantable medical devices, and applications that currently usesupercapacitor technology. The combination of high electronic and iontransport at reduced temperatures in these compounds also makes protonconducting analogs useful as electrode materials for otherelectrochemical applications such as low-temperature protonic fuel cellelectrodes or hydrogen gas separation membranes.

In some embodiments, electrodes are formed from any of the compoundsdescribed herein. In some embodiments, though not all, it may bepreferable for the electrode materials to be lithium storage compoundsother than one of ordered or partially ordered rocksalt crystalstructure type, or spinel crystal structure type, or vanadium oxide ormanganese oxide. Examples of ordered or partially ordered rocksaltcrystal structure types include LiCoO2, LiNiO2, LiMnO2, and their solidsolutions. Examples of spinel crystal structure type include LiMn2O4 andits solid solutions.

The electrode materials of the invention may have a variety of materialenergy densities at different charging or discharging rates. In one setof embodiments, the electrode has a material energy density that, whilecharging or discharging at a rate ≧800 mA per g of storage compound, isgreater than 250 Wh/kg, or charging or discharging at a rate ≧1.5 A perg of storage compound, is greater than 180 Wh/kg, or charging ordischarging at a rate ≧3 A per g of storage compound, is greater than 40Wh/kg, or charging or discharging at a rate ≧4.5 A per g of storagecompound, is greater than 10 Wh/kg.

In another set of embodiments, the electrode has a material energydensity that, while charging or discharging at a rate ≧800 mA per g ofstorage compound, is greater than 350 Wh/kg, or charging or dischargingat a rate ≧1.5 A per g of storage compound, is greater than 270 Wh/kg,or charging or discharging at a rate ≧3 A per g of storage compound, isgreater than 150 Wh/kg, or charging or discharging at a rate ≧4.5 A perg of storage compound, is greater than 80 Wh/kg, or charging ordischarging at a rate ≧6 A per g of storage compound, is greater than 35Wh/kg, or charging or discharging at a rate ≧7.5 A per g of storagecompound, is greater than 50 Wh/kg, or charging or discharging at a rate≧15 A per g of storage compound, is greater than 10 Wh/kg.

In another set of embodiments, the electrode has a material energydensity that, while charging or discharging at a rate ≧800 mA per g ofstorage compound, is greater than 390 Wh/kg, or charging or dischargingat a rate ≧1.5 A per g of storage compound, is greater than 350 Wh/kg,or charging or discharging at a rate ≧3 A per g of storage compound, isgreater than 300 Wh/kg, or charging or discharging at a rate ≧4.5 A perg of storage compound, is greater than 250 Wh/kg, or charging ordischarging at a rate ≧7.5 A per g of storage compound, is greater than150 Wh/kg, or charging or discharging at a rate ≧11 A per g of storagecompound, is greater than 50 Wh/kg, or charging or discharging at a rate≧15 A per g of storage compound, is greater than 30 Wh/kg.

Electrodes of the invention may have a variety of differentconfigurations depending on the application in which the electrode isused. In some cases, the electrode may comprise a sheet or a mesh coatedor impregnated with the storage compound. In other cases, the electrodecomprises a metal foil coated one or both sides with the storagecompound.

The electrode may include different loading amounts of the storagecompound. For example, the electrode may include a loading of at least 4mg, 8 mg, 10 mg, 14 mg, or 20 mg per square centimeter of projected areaof the sheet or mesh.

The electrode may be a sheet or a mesh having a total thickness of atleast 20 micrometers, 40 micrometers, 60 micrometers, 80 micrometers,100 micrometers, 150 micrometers, or 200 micrometers.

It should be understood that the electrodes of the invention may haveother configurations and structures than those described herein.

FIG. 28 schematicaly illustrates a storage battery cell 10 according toone embodiment of the present invention. Storage battery cell 10includes a positive current collector 12 in contact with a positiveelectrode 14. The storage battery cell further includes a negativecurrent collector 18 in contact with a negative electrode 16. Aseparator 20 is positioned between the positive electrode and thenegative electrode. Either the positive or the negative electrode (orboth) may be comprised of any of the compositions described herein.

Storage battery cells of the present invention may exhibit differentproperties. For example, the cell may exhibit, upon discharge, an energyof at least 0.25 Wh; in other cases, at least 1 Wh; in other cases, atleast 5 Wh; in other cases, at least 10 Wh; in other cases, at least 20Wh; in other cases, at least 30 Wh; in other cases, at least 40 Wh; inother cases, at least 60 Wh; and, in other cases, at least 100 Wh.

The storage battery cells may also exhibit a variety of combinations ofgravimetric energy and/or volumetric energy density upon discharge. Forexample, the storage battery cell may exhibit a discharge a gravimetricenergy density of at least 30 Wh/kg or a volumetric energy density of atleast 100 Wh/liter; a gravimetric energy density of at least 50 Wh/kg ora volumetric energy density of at least 200 Wh/liter; a gravimetricenergy density of at least 90 Wh/kg or a volumetric energy density of atleast 300 Wh/liter; a gravimetric power density of at least 500 W/kg ora volumetric power density of at least 500 W/liter; a gravimetric powerdensity of at least 1000 W/kg or a volumetric power density of at least1000 W/liter; a gravimetric power density of at least 2000 W/kg or avolumetric power density of at least 2000 Wh/liter.

Storage battery cells of the invention may also exhibit a variety ofgravimetric energy density at different power densities. For example,the storage cells may exhibit, upon discharge, a gravimetric energydensity of at least 30 Wh/kg at a power density of at least 500 W/kg, or20 Wh/kg at a power density of at least 1000 W/kg, or 10 Wh/kg at apower density of at least 1500 W/kg, or 5 Wh/kg at a power density of atleast 2000 W/kg, or 2 Wh/kg at a power density of at least 2500 W/kg, or1 Wh/kg at a power density of at least 3000 W/kg.

In another embodiment, the storage cells may exhibit, upon discharge, agravimetric energy density of 50 Wh/kg at a power density of at least500 W/kg, or 40 Wh/kg at a power density of at least 1000 W/kg, or 20Wh/kg at a power density of at least 2000 W/kg, or 10 Wh/kg at a powerdensity of at least 3000 W/kg, or 4 Wh/kg at a power density of at least4000 W/kg, or 1 Wh/kg at a power density of at least 5000 W/kg.

In another embodiment, the storage cells may exhibit, upon discharge, agravimetric energy density of at least 80 Wh/kg at a power density of atleast 1000 W/kg, or 70 Wh/kg at a power density of at least 2000 W/kg,or 60 Wh/kg at a power density of at least 3000 W/kg, or 55 Wh/kg at apower density of at least 4000 W/kg, or 50 Wh/kg at a power density ofat least 5000 W/kg, or 30 Wh/kg at a power density of at least 6000W/kg, or 10 Wh/kg at a power density of at least 8000 W/kg.

It should be understood that certain storage cells of the invention mayhave a variety of different structures than those described herein andexhibit different properties than those described herein.

The present invention will be further illustrated through the followingexamples, which are illustrative in nature and are not intended to limitthe scope of the invention.

EXAMPLE 1 Metal-Doped Compositions

This example demonstrates the preparation of compositions having theformulation Li(Fe_(1−a)M″_(a))PO₄, where M″ is Al, Ti, Zr, Mn, Nb, Ta,W, Mg, or Li. Specific compositions, heat treatments, and results arelisted in Tables 2 and 3, respectively. It was found that the electronicconductivity increased only for certain low concentrations of the metaladditive or dopant. The specific range of concentration providing a highelectronic conductivity (greater than about 10⁻⁵ S/cm) varied for eachdopant but was generally less than about 5 mole % of the Feconcentration. In addition to having a low concentration of the dopant,it was necessary to heat treat the material under conditions such thathigh electronic conductivity was obtained. These conditions includedheat treatment in a non-oxidizing gas atmosphere, including but notlimited to argon, nitrogen, and nitrogen-hydrogen mixtures. Moreover,the temperature of heat treatment was less than about 800° C. At 600°C., the firing time in the above described gas atmosphere was less thanabout 100 hours.

Sample Preparation

Compositions as listed in Table 2 or otherwise described herein wereprepared as follows or as adjusted to suit the particular composition byprocedures illustrated for the following compositions. The startingmaterials of this Example are listed in Table 1.

TABLE 1 Starting materials for a synthesis method for doped LiFePO₄Theoretical *Analyzed Manufacturer/Purity content content Compound (wt%) Element (wt %) (wt %) Li₂CO₃ Alfa-Aesar, 99.999 Li 18.8 18.9FeC₂O₄•2H₂O Aldrich, 99.99 Fe 31.0 30.7 NH₄H₂PO₄ Alfa-Aesar, 99.998 P26.9 27.2 *The metals content was analyzed using Direct Current Plasma(DCP) emission spectroscopy following ASTM E1097.

The starting materials were weighed to high precision using a laboratorybalance. For example, Zr-doped LiFePO₄ samples of the following dopinglevels and batch sizes were prepared using the following startingmaterials, wherein zirconium ethoxide served as the source of thedopant:

5 mole % Zr, 1 mole % Zr 2 mole % Zr 5 g batch 2.5 g batch 2.5 g batchNH₄H₂PO₄ 3.6465 g 1.7254 g 1.7254 g Li₂CO₃ 1.1171 g  0.554 g  0.554 gFeC₂O₄•2H₂O 5.4177 g 2.6715 g 2.6715 g Zr(OC₂H₅)₄ 0.4303 g 0.0407 g0.0814 g

Similarly, 1 mole % and 2 mole % Ti-doped LiFePO₄ were prepared usingthe starting materials as above, except that titanium methoxide,Ti(OCH₃)₄(CH₃OH)₂ was used as the source of Ti (in place of theZr(OC₂H₅)₄):

1 mole % Ti 2 mole % Ti 2.5 g batch 2.5 g batch NH₄H₂PO₄ 1.7254 g 1.7254g Li₂CO₃  0.554 g  0.554 g FeC₂O₄•2H₂O 2.6715 g 2.6715 gTi(OCH₃)₄(CH₃OH)₂ 0.0354 g 0.0708 g

Undoped LiFePO₄ samples were prepared from the same materials exceptwithout the dopant salt. For the other samples, with the dopants aslisted in Table 2, an appropriate metal salt was used. In particular, toprepare the Nb-doped samples, niobium phenoxide, Nb(OC₆H₅)₅, was used asthe dopant salt; to prepare the Ta-doped samples, tantalum methoxide,Ta(OCH₃)₅, was used as the dopant salt; to prepare the W-doped samples,tungsten ethoxide, W(OC₂H₅)₆, was used as the dopant salt; to preparethe Al-doped sample, aluminum ethoxide, Al(OC₂H₅)₃, was used as thedopant salt; and to prepare the Mg-doped samples, magnesium ethoxide,Mg(OC₂H₅)₂, was used as the dopant salt.

To prepare each sample, each of the components was weighed in anargon-filled glove box. They were then removed from the glove box andball milled, using zirconia milling balls, in a polypropylene jar forabout twenty hours in acetone. The milled mixture was dried at atemperature not exceeding 100° C., and then ground with a mortar andpestle in the argon-filled glove box. Each of the mixtures was then heattreated, given as “HT1” through “HT7” under the conditions listed inTable 3. In each case, a first heat treatment at 350° C. for ten hourswas conducted in a flowing atmosphere of the specified gas. Each of thepowder samples was then ground, using a mortar and pestle, and subjectedto a second heat treatment at a higher temperature, in a flowingatmosphere of the specified gas.

Conductivity Measurements

It is well-known that the electrical conductivity of solid compounds isdifficult to accurately measure from a finely divided powder form of thecompound. On the other hand, powders that have been compacted and firedso as to achieve sintered contacts between the powder particles, or havebeen partially or completely densified, allow more accurate measurementof the conductivity of the compound. For sintered pellets of reasonablyhigh density, and in which the particle contacts do not have a higherspecific resistance, the conductivity of the pellet is reduced from thatof the compound itself in approximately linear proportion to the amountof porosity that is present. For example, a pellet that has 10% porositymay be judged to have about 90% of the conductivity of the compound. Inorder to measure the conductivity when samples were prepared in a powderform, pellets were pressed out of the heat treated powder sample priorto the second heat treatment, and placed in alumina crucibles during thesecond heat treatment so that the powders and sintered pellets were heattreated together. The density of the fired pellets were from about 60%to about 95% of the crystal density, depending on composition and heattreatment.

In order to measure electrical conductivity, 2-point and 4-point (vander Pauw, vdP) conductivity measurements were performed according toknown conventional procedures. Because metal contacts that are blockingto lithium ions and conductive to electrons were used, the resultingconductivities are understood to reflect the electronic conductivity ofthe compound. The room temperature conductivities of several of thedoped samples are listed in Table 2.

X-ray Diffraction, Electron Microscopy, Specific Surface AreaMeasurement, and Chemical Analysis

Several methods were used to determine the crystalline phase, extent ofcrystallization, powder particle size and morphology, specific surfacearea of the powder, and the location of dopants. Samples were evaluatedby x-ray diffraction after heat treatment to determine the crystallinestructure as well as to determine if there was a detectable secondaryphase. In some cases, some of the powder samples were examined at higherresolution by transmission electron microscopy (TEM) and/or scanningtransmission electron microscopy (STEM) to determine whether secondaryphases were present, whether a surface coating of another phase werepresent, and to measure the concentration of the dopant metal within thecrystalline grains of the LiFePO₄ phase. This allowed a determination ofwhether the metal dopant, at the added concentration and heat treatment,was soluble or had exceeded its solubility limit in the LiFePO₄ phase.It was also possible to determine whether the particles of crystallizedcompound had a surface coating of another material. In some cases, thecomposition of the powders or pellets were determined using directcurrent plasma (DCP) emission spectroscopy according to ASTM ASTM E1097,or combustion IR detection according to ASTM E1019.

In the samples listed in Table 2, the first numeral indicates thedopant, the second the concentration, and the third, the heat treatment.For example, sample 3c1 refers to a Ti-doped sample of 0.1 mole %concentration subjected to the heat treatment HT1. Where theconcentration of dopant is given herein in mole percent, it refers tothe relative molar fraction, Ti/(Ti+Fe) multiplied by 100.

TABLE 2 Results for Undoped and Doped Lithium Iron Phosphates RoomTemperature Conductivity (S/cm) XRD/TEM/ Minor Composition Heat van derSTEM phases (Sample) Treatment 2-point Pauw observations (by XRD) 1.Undoped (1a1) HT1 <10⁻⁶ — Single phase None detected LiFePO₄ olivine(1b2) HT2 <10⁻⁶ — Single phase None detected LiFePO₄ olivine (1c3) HT3<10⁻⁶ — Single phase None detected LiFePO₄ olivine (1d6) HT6  2.2 ×10^(−9†) — Single phase None detected LiFePO₄ olivine (1e6) HT6 3.74 ×10^(−10‡) — Single phase None detected LiFePO₄ olivine (1f7) HT7 2.22 ×10^(−9†) — — — LiFePO₄ (1g8) HT8  1.8 × 10⁻¹⁰ — Multi-phase Li₃PO₄, Fe₃PLiFePO₄ 2. Aluminum (2a1) HT1  8.2 × 10⁻⁵ — Dopant soluble None detectedLi(Al_(.002)Fe_(.998))PO₄ (2b6) HT6 ~10⁻³ — Dopant soluble None detected(Li.₉₉Al_(.01))FePO₄ 3. Titanium (3c5) HT5 <10⁻⁵ — Dopant soluble Nonedetected Li(Ti_(.001)Fe_(.999))PO₄ (3d1) HT1  1.7 × 10⁻⁴ — Exceeds Notidentified Li(Ti_(.002)Fe_(.998))PO₄ solubility (3e1) HT1  2.0 × 10⁻⁴ —Exceeds Li₃PO₄ Li(Ti_(.01)Fe_(.99))PO₄ solubility (3e2) HT2  1.9 × 10⁻⁴— Exceeds Li₃PO₄ Li(Ti_(.01)Fe_(.99))PO₄ solubility (3e3) HT3 <10⁻⁶ —Exceeds Not identified Li(Ti_(.01)Fe_(.99))PO₄ solubility (3f2) HT2  1.4× 10⁻⁶ — Exceeds Not identified Li(Ti_(.02)Fe_(.98))PO₄ solubility (3g6)HT6  1.3 × 10^(−3‡) — Dopant soluble None detected(Li_(.99)Ti_(.01))FePO₄ (3g7) HT7  2.3 × 10^(−2‡) — Exceeds Li₃PO₄, Fe₂P(Li_(.99)Ti_(.01))FePO₄ solubility 4. Zirconium (4a1) HT1  5.0 × 10⁻⁵ —Dopant soluble None detected Li(Zr_(.002)Fe_(.998))PO₄ (4b1) HT1  3.7 ×10⁻⁴ — Exceeds Li₃PO₄ Li(Zr.₀₁Fe_(.99))PO₄ solubility (4b2) HT2  4.5 ×10⁻⁵ — Exceeds Li₃PO₄ Li(Zr_(.01)Fe_(.99))PO₄ solubility (4b3) HT3 <10⁻⁶— Exceeds Not identified Li(Zr_(.01)Fe_(.99))PO₄ solubility (4c2) HT2 1.8 × 10⁻⁴ — Exceeds Li₂ZrO₃ Li(Zr_(.02)Fe_(.98))PO₄ solubility (4d2)HT2 ~10⁻⁵ — Exceeds Li₂ZrO₃ Li(Zr_(.05)Fe_(.95))PO₄ solubility (4e1) HT1~10⁻⁴ — Dopant soluble None detected (Li_(.99)Zr_(.01))FePO₄ (4e2) HT8 1.6 × 10⁻² — Exceeds Li₃PO₄, Fe₂P (Li_(.99)Zr_(.01))FePO₄ solubility 5.Niobium (5b1) HT1  1.3 × 10⁻⁴ — Dopant soluble None detectedLi(Nb_(.001)Fe_(.999))PO₄ (5c1) HT1  5.8 × 10⁻⁴ — Dopant soluble Nonedetected Li(Nb_(.002)Fe_(.998))PO₄ (5c4) HT4 <10⁻⁶ — — —Li(Nb_(.002)Fe_(.998))PO₄ (5e6) HT6  1.1 × 10⁻³ — Dopant soluble Nonedetected (Li_(.998)Nb_(.002))FePO₄ (5e7) HT7  1.1 × 10^(−2‡) — Dopantsoluble None detected (Li_(.998)Nb_(.002))FePO₄ (5f6) HT6  4.1 × 10⁻² —Dopant soluble None detected (Li_(.995)Nb_(.005))FePO₄ (5g6) HT6  2.2 ×10⁻² 2.73 × 10⁻² Dopant soluble None detected (Li_(.99)Nb_(.01))FePO₄(5g7) HT7  4.3 × 10^(−2‡) — Exceeds Li₃PO₄, Fe₂P (Li_(.99)Nb_(.01))FePO₄solubility (5h6) HT6  2.8 × 10⁻³ — Exceeds Fe₂P (Li_(.98)Nb_(.02))FePO₄solubility (5i6) HT6 ~ 10⁻⁶ — Exceeds Fe₂P (Li_(.96)Nb_(.04))FePO₄solubility 6. Tantalum (6a1) HT1  3.0 × 10⁻⁵ — Dopant soluble Nonedetected Li(Ta_(.002)Fe_(.998))PO₄ 7. Tungsten (7a1) HT1  1.5 × 10⁻⁴ —Dopant soluble None detected Li(W_(.002)Fe_(.998))PO₄ 8. Magnesium (8a1)HT1 ~10⁻⁴ — Dopant soluble None detected Li(Mg_(.002)Fe_(.998))PO₄ (8b6)HT6  6.8 × 10^(−4‡) — Dopant soluble None detected(Li_(.99)Mg_(.01))FePO₄ (8b7) HT7  2.4 × 10^(−2‡) — Exceeds Li₃PO₄, Fe₂P(Li_(.99)Mg_(.01))FePO₄ solubility (8b8) HT8  3.8 × 10^(−3‡) — ExceedsLi₃PO₄, Fe₂P (Li_(.99)Mg_(.01))FePO₄ solubility 9. Manganese (2+) (9a1)HT1 ~10⁻⁴ — Dopant soluble None detected Li(Mn_(.002)Fe_(.998))PO₄ 10.Iron (2+) (10a6) HT6 <10⁻⁶ — Exceeds Li₃PO₄, Fe, (Li_(.99)Fe_(.01))FePO₄solubility Fe₃P 11. Iron (3+) (11a6) HT6  3.3 × 10⁻² 4.1 × 10⁻² ExceedsLi₃PO₄, Fe, (Li_(.99)Fe_(.01))FePO₄ solubility Fe₃P 12. Lithium (12a6)HT6 <10⁻⁶ — Exceeds Li₃PO₄, Fe, Li(Fe_(.99)Li_(.01))PO₄ solubility Fe₃P^(†)measurement by AC Impedance Spectroscopy ^(‡)measurement by twopoint method, using sputtered Au electrodes.

TABLE 3 Heat Treatment Conditions Heat Conditions Treatment (all gasesat 1 atm total pressure) HT1 350° C., 10 hours, Ar 600° C., 24 hours, Ar— HT2 350° C., 10 hours, N₂ 600° C., 24 hours, N₂ — HT3 350° C., 10hours, N₂ 800° C., 24 hours, N₂ — HT4 350° C., 10 hours, N₂ 800° C., 24hours, N₂ — HT5 350° C., 10 hours, Ar 600° C., 24 hours, Ar 600° C., 76hours, Ar HT6 350° C., 10 hours, Ar 700° C., 20 hours, Ar — HT7 350° C.,10 hours, Ar 850° C., 20 hours, Ar — HT8 350° C., 10 hours, Ar 800° C.,15 hours, ArResults

X-ray diffraction showed that after the 350° C. heat treatment, thepowders of this example were poorly crystallized and not of a singlemajor crystalline phase. After the second, higher temperature heattreatment, all samples subjected to XRD showed peaks associated with theolivine structure. The relative intensity of X-ray peaks showed that theolivine phase was the major crystalline phase. Visual observation of theheat treated powders and pellets proved to be a reliable indication ofwhether or not increased electronic conductivity had been obtained.While the undoped LiFePO₄ was light to medium gray, the conductive dopedpowders and sintered pellets, regardless of specific dopant,concentration, or heat treatment, were colored black. Conductivesintered pellets were also easily distinguished from insulating pelletswith a simple ohmmeter measurement using two steel probes placed 0.5-1cm apart. Insulating compositions had resistances too great to measure(being greater than the instrument limit of 200 MΩ), while conductivesamples had resistances of typically 30 kΩ to 300 kΩ.

The results in Table 2 show that heat treating undoped LiFePO₄ was noteffective in producing an acceptable conductive material; each of theconductivities of sintered pellets was less than about 10⁻⁶ S/cm. Theundoped compound was also found to have a very narrow range of cationnonstoichiometry, with as little as 1% deficiency of the ferrous ironoxalate resulting in a detectable amount of Li₃PO₄ phase.

In contrast, for the dopants listed, at low concentrations, it waspossible to produce a sample having a room temperature conductivitygreater than about 10⁻⁵ S/cm. These conductivity values exceed knownvalues for the positive electrode compound LiMn₂O₄. Further, Al, Ti, Zr,Nb, W, Mg, Mn, and Fe(3+)-doped samples could be produced with aconductivity greater than 10⁻⁴ S/cm.

Electron microscopy showed that the highly electronically conductivesamples did not have a surface coating or other form of an additionalconductive phase. A typical image is shown in FIG. 1, which is a copy ofa TEM image of a 0.01% Ti-doped sample.

The figures show that the doped compositions of LiFePO₄, synthesized innon-oxidizing or inert atmosphere at temperatures below about 800° C.,had increased electronic conductivity compared to the undoped LiFePO₄compositions, thus making them useful as lithium storage electrodesespecially at practical charge/discharge rates. At the low doping levelsused, the doping does not limit the ability of the material to storelithium at a high voltage (about 3.5V relative to lithium metal) orachieve a high lithium storage capacity.

The results also showed that too high a heat treatment temperature,and/or too long a heat treatment period, can result in insulatingmaterials. As a specific comparison, the Ti-doped sample, sample 3e3,which was heat treated at 800° C. for twenty-four hours, was insulating(less than 10⁻⁶ S/cm) whereas a similar 1% Ti-doped composition, samples3e1 and 3e2, which were heat treated at 600° C. for twenty-four hours,were highly conductive (2×10⁻⁴ and 1.9×10⁻⁴ S/cm). The insulating sample3e3 was examined using an STEM, which showed that, unlike the conductivesamples, the amount of Ti in solid solution in the parent phase was notdetectable (by energy-dispersive x-ray analysis). Titanium appeared toaggregate as a second phase, as shown in FIG. 2 (right side images).Thus, a high temperature heat treatment can cause the dopant to becomeinsoluble. Similarly, the Zr-doped sample, 4b3, was also heat treated at800° C. for twenty-four hours, and was insulating (less than 10⁻⁶ S/cm).A similar 1% Zr-doped composition, which was heat treated at 600° C. fortwenty-four hours in argon or nitrogen, 4b1 and 4b2, was conductive. TheNb-doped sample, 5c4, was heat treated at 800° C. for twenty-four hoursand was found to be insulating, whereas a similar 0.2% Nb-dopedcomposition that was heat treated at 600° C. for twenty-four hours inargon or nitrogen, 5a1 and 5b1, was highly conductive. Copies of STEMimages of the Nb-doped samples are shown in FIG. 3. Notably, Nb appearsto have a higher solubility limit than either Ti or Zr.

Moreover, even at a lower heat treatment temperature (600° C.), too longa heat treatment time can convert a conductive composition to insulatingcomposition. For example, sample 3c5 was initially heat treated at HT1.A pellet was then pressed and heat treated an additional 76 hours, inargon, and was found to be less conductive relative to sample 3c1, whichhad a similar composition but was not heat treated an additional 76hours.

Further, the results also showed that there is a dopant limit and thattoo much dopant can result in an insulating composition. For example, a2 mole % Ti-doped composition, 3f2, is less conductive than a 1 mole %Ti-doped composition, 3e2. Notably, a 2 mole % Zr-doped composition,4c2, is still relatively conductive, if not more conductive, compared toa 1 mole % Zr-doped composition, 4b2. However, increasing the Zrconcentration to 5 mole %, as in sample 4d2, reduced the conductivity.X-ray diffraction analysis showed that the 5 mole % Zr-doped sample hada small amount of secondary phase, which appeared to be Li₂ ZrO₃. Incontrast, the 2 mole % Zr-doped sample had peaks, corresponding to thelatter phase, which were negligible, as shown in FIG. 4.

Further, the results showed that the powders prepared were free ofcoatings of carbon or other conductive additive phases. TEM and STEMshowed that the powders of Examples 1 and 2 typically contained a smallfraction of unreacted precursors in addition to the majority phase ofthe olivine structure. However, TEM images at resolution levels highenough to image the lattice planes of the olivine phase, an example ofwhich is shown in FIG. 5, showed that the surfaces of the particles werenot coated with another distinguishable phase of material. Thus theincreased conductivity of the conductive powders of this Example wasobtained in the absence of a continuous phase of a conductive additive.

Other polyanion compounds, aside from those having the olivinestructure, such as those of the NASICON VOPO₄, LiFe(P₂O₇) or Fe₄(P₂O₇)₃structures, can be similarly doped and synthesized to achieve highelectronic conductivity. Further, based on the results obtained using Mgas a dopant, it is believed that other Group IIA alkaline earth metals,such as Be, Ca, Sr, and Ba, should have similar effects. Based on theresults obtained using Ti and Zr, which are Group IVA elements, it isbelieved that other Group IVA elements, such as Hf, should have similareffects. Based on the results obtained using Nb and Ta, which are GroupVA elements, it is believed that other Group VA elements, such as V,should have similar effects. Based on the results obtained using W,which is a Group VIA element, it is understood that other Group VIAelements, such as Cr and Mo, should have similar effects. Based on theresults obtained using Al, it is believed that other Group IIIBelements, such as B, Ga, and In, should have similar effects.

EXAMPLE 2 Lithium Deficient and Substituted Compositions

Several compositions were prepared with an overall composition of theformula Li_(1−a)M″_(a)FePO₄, included in Table 2. The starting materialsand synthesis procedure of Example 1 were used, with the exception thatboth plastic and porcelain milling containers were used with thezirconia milling media. Because the abrasion of polymeric millingcontainers and milling media can be a source of carbon, the porcelaincontainers were used to compare results with and without this potentialcarbon source.

As shown in Table 2 and also in Table 4, the doped samples of thisdoping formulation generally had higher conductivity than those ofExample 1, with room-temperature conductivities of as much as about4×10⁻² S/cm being measured by a two-point method (samples 5f6 and 5 g7).Highly conductive samples were obtained using either plastic orporcelain milling containers, showing that excess carbon added from themilling container is not necessary to achieve such conductivities. Theresults show that introducing Li/metal cation nonstoichiometry canpromote Li deficiency, relative to the ideal LiMPO₄ stoichiometry,which, combined with doping with selected metals, can increaseelectronic conductivity. Also, higher temperature heat treatments, suchas HT6 and HT7, can be used with these lithium-deficient cationstoichiometry compositions without losing electronic conductivity orexsolving the dopant, in comparison to the LiFe_(1−a)M″_(a)PO₄compositions (Example 1). STEM observations showed that compositionsexhibiting a detectable concentration of the added dopant in thecrystalline LiFePO₄ grains were conductive.

Compositions Li_(1−x)M_(x)FePO₄, that, while not being bound by anyparticular crystal chemical interpretation, have a formulation thatallows substitution onto the M1 sites by a cation supervalent to Li⁺,exhibited higher solubility for several dopants (Mg²⁺, Al³⁺, Ti⁴⁺, Nb⁵⁺,and W⁶⁺) than did compositions LiFe_(1−x)M_(x)PO₄. FIG. 6 compares theX-ray diffraction patterns for several 1 mol % doped powders of eachcation stoichiometry; in each case the lithium-deficient stoichiometry(FIG. 6 a) exhibits no detectable impurity phases. By contrast, sampleswith the same dopants and concentrations in the iron-deficientstoichometry showed detectable precipitation of Li₃PO₄ by XRD (FIG. 6 b)and impurity phases enriched in the dopant, using electron microscopy.FIG. 7 shows an example of the first stoichiometry,Li_(0.99)Nb_(0.01)FePO₄, in which elemental mapping shows a uniformdistribution of the Nb dopant. The amount of the dopant in solidsolution may be less than the total amount of dopant added to thesample. For example, in the Li_(1−a)Nb_(a)FePO₄ compositions, heattreated at 850° C., a concentration x about 0.0023 was detected in solidsolution for an overall composition a about 0.01. This shows that thesolid solubility was limited to about a=0.0023 at 850° C. Nonetheless,compositions with a values, both greater than or less than 0.0023, weremade conductive. In the Li_(x)(Fe_(1−a)M″_(a))PO₄ compositions, samplesprocessed at 600° C. were conductive while those processed at 700° C.and higher were not. Correspondingly, the samples processed at 600° C.had detectable dopants in solid solution when examined by STEM, whilethose processed at 700° C. did not.

The observed results that the increase in conductivity is not directlyproportional to dopant concentration is consistent with a limited dopantsolubility in some cases. That is, for those dopants that increasedelectronic conductivity, there was a large increase in conductivity atlower doping levels and weaker conductivity-concentration dependence atslightly higher dopant levels. For example, in the case ofLiFe_(1−a)M″_(a)PO₄, the greater than 100 times increase inconductivity, compared to the undoped material, at dopant concentrationsas low as 0.02% (for M″=Ti, Nb, and Mg), is followed by much smallerchanges in conductivity with further increases in dopant concentration.For compositions Li_(1−a)M″_(a)FePO₄, the electronic conductivity isfirstly higher overall by at least about an order of magnitude than forany of the LiFe_(1−a)M″_(a)PO₄ compositions. Compared to the undopedmaterial, the increase in conductivity is significant, greater by afactor of more than 10⁷ times, with a doping level as low as 0.2%(Nb-doped). However, further doping increases the conductivity onlymodestly.

Materials were also synthesized that contained an excess of Fe,typically in the form of an Fe²⁺ or Fe³⁺ salt, as shown in Table 2.While an excess of either Fe²⁺ or Fe³⁺ can be substituted into thecomposition Li_(1−a)M″_(a)FePO₄, as with the other dopants M″, a certainconcentration must be in solid solution (i.e., form part of the crystallattice) for the conductivity to be increased substantially, since thisdetermines the electronic carrier concentration. The results with Fe²⁺and Fe³⁺ doping are consistent with the experiments using other dopantsM″ that show that when conductivity increased, the dopant in questionwas found to be in solid solution (either through STEM measurements ofdopant distribution in the crystallites or by the appearance/absence ofimpurity phases by STEM or XRD).

Further, it is believed that the solubility of dopants M″ is a functionof ion size. With the exception of Mn²⁺, all of the dopants that can beeffective as M′ dopants have an ionic radius, in octahedralcoordination, that was less than that of Fe²⁺. This is supported by thefollowing ionic radii values, taken from the tabulation by Shannon(1976):

R(Fe²⁺) = 0.78 A R(Li⁺) = 0.76 A R(Fe³⁺) = 0.65 A R(Mg²⁺) = 0.72 AR(Mn²⁺) = 0.83 A R(Ti⁴⁺) = 0.61 A R(Zr⁴⁺) = 0.72 A R(Nb⁵⁺) = 0.64 AR(Ta⁵⁺) = 0.64 A R(W⁶⁺) = 0.60 A R(Al³⁺) = 0.54 A

The temperature dependence of conductivity in the materials of theinvention was measured using 2-point and 4-point electrical conductivitymeasurements of fired pellets pressed from powder samples preparedaccording to Examples 1 and 2. Both undoped and doped compositions weremeasured. In addition, ac (impedance spectroscopy) measurements weremade on pellets prepared from undoped powder. The temperature dependenceof electrical conductivity is shown in FIGS. 8 and 9 as a plot of log₁₀conductivity against 1000/T(K). It is seen that the doped compositionscan have more than 10⁷ greater conductivity than an undoped sample.While both types exhibited increasing conductivity with increasingtemperature, indicating semiconducting behavior, the doped materials hadmuch shallower temperature dependence. An activation energy in the rangeof 25-75 meV was determined for the highly conductive doped samples,which is reasonable for ionization of shallow acceptors or donors, whilean activation energy of about 500 meV was observed for the undopedsample. The high conductivity of the doped samples is maintained, withlittle temperature dependence, over the −20 C to +150 C temperaturerange of interest for many battery applications. Near room temperature,for example between 21 C to 27 C, the variation of electronicconductivity with temperature is minor, such that where a temperaturewithin this range is referred to herein, it is understood that a rangeof temperatures around any particular value is included.

The highly conductive samples were also subjected to a Seebeckcoefficient measurement. Platinum leads were attached to two ends of asintered sample, whereupon one end was heated to a higher temperaturethan the other end, and the induced voltage was measured. The heated endwas found to be at a negative potential relative to the cold end,exhibiting easily measured and significant potential values of −0.1 mVto −0.3 mV. This shows that the conductive LiFePO₄ compositions werep-type conductors. An undoped LiFePO₄ composition subjected to the samemeasurement was found to be n-type.

In some cases, the electrical conductivity of the samples was measuredusing a four-point microcontact method in order to determine theconductivity of individual crystalline grains. For these measurements,densely sintered pellets with an average grain size of about 10micrometers were cut and polished. A co-linear array of microcontactswere used. Current probes were placed about 100 micrometers apart on thepolished surface, while voltage probes were placed about 10 micrometersapart. FIG. 10 shows three samples whose conductivities at themicroscopic scale were measured, two being 1% Nb-doped conductivecompositions sintered at 850 C and 900 C respectively, and one being anundoped composition sintered at 900 C Combustion IR detection showedthat all three samples had low carbon content, less than 0.5 wt %. Thegray phase in FIG. 10 is the olivine phase, the black contrast featuresare porosity, and the bright contrast particles are iron phosphidephase. FIG. 11 shows the microcontact measurement geometry, in which itis seen that the inner voltage contacts are about 10 micrometers apart,or about the same separation as individual grains in the samples of FIG.10. Thus the voltage contacts typically span one grain or one grainboundary. The microcontact array was placed in 12 to 15 separatelocations on each sample, and the current-voltage relationship wasmeasured at teach point over a range of currents in a room-temperaturelaboratory. FIG. 12 shows histograms of the conductivity obtained fromthe measurements, in which each bar represents one location of themicrocontact array. It is seen that firstly, within each sample theconductivity has a similar value from place to place showing relativelyuniform conductivity across a sample. Secondly, the conductivity of thedoped samples is of about the same magnitude as measured by two-pointand four-point measurements across entire sintered pellets, and isseveral orders of magnitude greater than the conductivity of the undopedsample.

TEM observations were made of the powders of Example 2. FIG. 13 showscopies of TEM images of powders doped with 1% Nb or 1% Zr. It is seenthat the average size of individual crystallites is less than about 100nm in the Nb-doped sample, less than about 50 nm in the Zr-doped sample,and that the powder has an aggregated morphology. Energy-dispersiveX-ray analysis was conducted to determine the location of residualcarbon, typically present at a level determined by combustion IRanalysis to be between 0.2 and 2.5 wt % depending on the firingconditions. FIG. 14 shows TEM images and corresponding chemical analysesof regions in a 1% Nb doped sample fired at 600 C and that was analysedto have about 2.4% residual carbon. This sample of relatively highresidual carbon content compared to others of Example 2 was selected forTEM in order to determine if a carbon coating on the particles aspracticed in prior art was present. FIG. 14 shows a particle ofunreacted precursor, present in small amounts in the sample, in whichcarbon is found at an enriched level. In the other regions, containingthe olivine phase, no carbon is detected. FIGS. 15 and 16 show highresolution TEM images of olivine phase particles, in which latticefringes are imaged. No continuous surface phase of carbon or otherseparate conductive compound was found. Thus it is seen that the fineparticle size and increased conductivity of these samples is observed insamples without a significant amount of free carbon.

Surface area measurements are another well-known measure of effectiveparticle size. The specific surface area was measured, using the BETmethod, of doped and undoped samples heat treated under severalconditions. Table 4 shows results for several powder samples. It isobserved that the undoped powders have a specific surface area that istypically less than about 10 m²/g for heat treatment temperatures of600° C. or greater. These are heat treatment conditions sufficient toprovide a nearly completely crystallized powder. However, the dopedcompositions have much higher surface area, typically greater than 40m²/g for 1% Zr-doped powder fired at 600 C, and greater than m²/g for 1%Nb-doped powder fired at 600 C In the doped samples the powder is alsonearly completely crystallized after firing at these temperaturesalthough a small quantity of incompletely crystallized precursor to theolivine phase remains. Other powders doped with 0.2-1 mole % of dopantssuch as Al, Mg, and Ti also had specific surface areas of 35 to 42 m²/gafter firing at 600 C. At higher firing temperatures of 700 to 800° C.the specific surface area of the doped samples remains higher than ofthe undoped samples. Having a crystal density of 3.6 g/cm³, the diameterof monosized spheres of the compound having an equivalent specificsurface area (i.e., the equivalent spherical particle size) of 40 m²/gis 21 nm, of 30 m²/g is 28 nm, of 29 m²/g is 42 nm, of 15 m²/g is 56 nm,of 10 m²/g is 83 nm, of 5 m²/g is 167 nm, and of 1 m²/g is 833 nm. Thusit is seen that the doping methods of the present example provide forcomplete or nearly complete crystallization of the olivine structurecompound while also providing for a high specific surface area, higherthan that of the undoped compound under identical processing and firingconditions.

TABLE 4 Compositions, Firing Conditions, and Specific Surface Areas ofInsulating and Conductive Samples BET area Temp. (m²/ Composition (° C.)Container g) Conductivity Color LiFePO₄ 600 Plastic bottle 9.5insulating Gray 700 Porcelain jar 3.9 insulating Gray 800 Porcelain jar~1 insulating Light Gray LiFe_(0.99)Zr_(0.01)PO₄ 600 Porcelain jar 43.2conductive Black 600 Porcelain jar 41.8 conductive Black 700 Porcelainjar 26.4 conductive Black 750 Porcelain jar 11.6 conductive Dark grayLiFe_(0.99)Nb_(0.01)PO₄ 600 Porcelain jar 34.7 conductive Black 800 PPorcelain jar 15.3 conductive Black

Without being bound by any particular interpretation, these results showthat conductivities, higher than those obtained using the method andcompositions of Example 1, can be obtained in a composition that isdeficient in the alkali ion and excess in the other metals that wouldnormally occupy octahedral sites in a LiFePO₄ structure. As mentioned,the results show that the solubility of the metal, M″, was higher whenthe composition was formulated in this manner. Without being bound byany interpretation, it is reasonable to expect that having a deficiencyof Li and excess of Mg allows one or the other octahedral site cations,Mg or Fe, to occupy octahedral sites in the structure that wouldnormally be occupied by Li.

Based on the results obtained in this instance, where there is an excessof the non-alkaline metal and a deficiency of the alkali, it is believedthat almost any metal added to the structure of the parent compound suchthat substitution of the metal onto the M1 crystallographic sitesnormally occupied by the main alkaline metal occurs, would have thedesired effect of improving the electronic conductivity of the resultingcompound.

Without being bound by any particular interpretation, we note thatLiFePO₄ is found by first-principles calculations of the spin-polarizedtype to have an unusual band structure of the type known as ahalf-metal. The band gap is spin-sensitive and may in one spin have agap of about 1 eV while in the other being a metal. It is also foundthat the electron effective mass is much larger than the hole effectivemass, which is consistent with observation of higher electronicconductivity in a p-type conductor.

Without being bound by any particular interpretation, it is noted that amechanism of defect formation can be understood from the observationsthat the increased electronic conductivity of the present materials isthermally activated and p-type, that there is not a strictproportionality between dopant concentration and conductivity, thatsimilar increases in conductivity are possible for dopants of 2+ through6+ valence, that a two-phase reaction exists upon delithiation, as shownin later Examples and as is seen in undoped LiFeO₄, and that a highcapacity and high rate capability are maintained over a wide range oflithiation of the doped compounds. The olivine structure has continuousnetworks of metal-filled anion polyhedra, including having the cationsthat occupy the M2 sites (Fe site in LiFePO₄) forming a corner-sharingnetwork of octahedra in the (010) plane, while the cations on M1 (Li)sites form edge-sharing chains of octahedra in the [100] direction. Itis noted that the substitution of a cation M that is supervalent to Li⁺in the composition Li_(1−x)M_(x)FePO₄ is normally expected to result indonor doping. In oxides, aliovalent solutes can be compensated byelectronic or ionic defects. The following point defect reactions (inKröger-Vink notation), illustrate these mechanisms for an M³⁺ cationthat is respectively compensated by electrons or by cation vacancies onthe M2 site:½M₂O₃+FeO+½P₂O₅

M_(Li) ₋₋ +Fe_(Fe) ^(x)+P_(P) ^(x)+4O_(O) ^(x)+2e′+½O₂(g)  (1)½M₂O₃+½P₂O₅

M_(Li) ₋₋ +V_(Fe)″+P_(P) ^(x)+4O_(o) ^(x)  (2)

In the first instance, electroneutrality is given by [M_(Li) ₋₋ ]=n,namely the dopant acts directly as a donor species. If the secondmechanism is dominant, electroneutrality is given by [M_(Li) ₋₋]=2[V_(Fe)″], in which case the donor and vacancy charge-compensate oneanother and no direct effect on the electronic carrier concentration isexpected. However, it can be shown that in this instance as well,secondary defect equilibria should lead to an increase in the n-typeconductivity. Neither of these simple mechanisms can explain a materialof high p-type conductivity. An excess of acceptor point defects aboveand beyond the dopant concentration, or a large difference between holeand electron mobilities as discussed earlier, are necessary. Possibleacceptors in the LiFePO₄ structure are cation vacancies (V_(Li)′,V_(Fe)″), or oxygen interstitials (O_(i)″). The latter defect isunlikely given the nearly hexagonal close-packed oxygen sublattice inolivine, which should result in a high anion vacancy formation energy.

A mechanism whereby cation doping on the M1 sites allows thestabilization of solid solutions with a net cation deficiency, that is,where the doped olivine end member has a solid solution of compositionLi_(1−a−x)M_(x)FePO₄ or Li_(1−x)M_(x)Fe_(1−b)PO₄, in which a and b areM1 or M2 vacancy concentrations respectively, is consistent with theresults. If the net charge due to a and b exceed that due to x, then thematerial will have a net excess of acceptor defects (Fe³⁺ ions). Takingfor example an M³⁺ dopant, the respective valences for a lithiumdeficient solid solution are Li¹⁺ _(1−a−x)M³⁺ _(x)(Fe²⁺ _(1−a+2x)Fe³⁺_(a−2x))(PO₄)³⁻. It is noted that lithium deficiency is particularlylikely under high temperature firing conditions due to lithiumvolatility. The above defect mechanism is analogous to allowing anextension of the solid solution field for the pure Li-rich end memberphase to cation deficient solid solutions, Li_(1−a)FePO₄. We recall thatpure LiFePO₄ has been observed to decompose immediately to twoco-existing phases upon delithiation, LiFePO₄ and FePO₄, thereby pinningthe Li chemical potential and resulting in the flat intercalationvoltage vs. lithium concentration. Thus the insulating behavior ofundoped LiFePO₄ throughout electrochemical cycling suggests negligiblemixed (Fe²⁺/Fe³⁺) iron valency in either phase. The retention of eitherlithium or iron deficiency in the highly lithiated solid solution cantherefore result in charge compensation by Fe³⁺ and p-type conductivity.

Regarding the delithiated FePO₄ end member phase, our electrochemicaldata in later Examples indicate that it also retains high electronicconductivity throughout cycling. The influence of M1 site cation dopingis expected to be quite different for this phase. Starting with pureFePO₄, in which all iron is trivalent, cation doping will result in theformation of divalent iron: M³⁺ _(x)(Fe²⁺ _(3x)Fe³⁺ _(1−3x))PO₄. Thiscomposition is obtained upon delithiation of the solid solution givenearlier. The dopant in this instance may be viewed as an “interstitial”cation donor, occupying normally unoccupied M1 sites, and n-typeconductivity should result. During operation as a lithium storagematerial, the present materials may be a two-phase material, one phasep-type and the other n-type, that change in their relative proportionsas the overall lithium concentration changes. A transition from p- ton-type conductivity may be measurable for the two-phase material as awhole as delithiation proceeds. This behavior may be observed whetherthe cation dopant M occupies the M1 site, or preferentially occupies theM2 site and displaces Fe to the M1 site.

The room temperature conductivity of some of the compounds of theinvention exceeds that of the well-established intercalation cathodesLiCoO₂ and LiMn₂O₄ in their lithiated (discharged) states. At these highlevels of electronic conductivity, lithium ion transport is likely tolimit the overall rate of intercalation and deintercalation. That is,the effective lithium chemical diffusion coefficient is likely to belimited by lithium transport (i.e., the ionic transference number t_(Li)is ˜0). Because it is known that delithiation of LiFePO₄ results incoexistence of two phases, lithium ingress and egress from particles ofthe storage material requires growth in the amount of one phase and adecrease in the amount of the other. Without being bound by anyparticular interpretation of the rate-limiting microscopic mechanism ofphase transformation, it is understood that a decrease in thecrystallite size is beneficial to ion transport. At the same time, it isnecessary to simultaneously accommodate electron flow to and from theparticles. The structure of the materials of the invention are almostideal for providing optimal mixed electronic-ionic transport in abattery system, having a porous aggregate structure in which thenanoscale primary crystallites can be surrounded by the electrolyte,allowing lithium ion transport through a very small cross-sectionaldimension, while remaining electronically “wired” together through thesinter necks. For materials in which electronic transport is limiting,it can still be beneficial to decrease the crystallite size, as thepotential drop across particle is less for a material of higherconductivity. (If ion transport is limiting, further increases in theelectronic conductivity are not expected to improve the rate capabilityof a single particle significantly, but can improve the electronicconductivity of a network of particles such as that present in a typicalcomposite electrode.)

Having a fine primary crystallite size due to doping as provided by thepresent invention provides high rate capability. Therefore, anotherfeature of the materials of the present invention is a structurecharacterized by primary crystallites having at least a smallestdimension that is less than 200 nm, preferably less than 100 nm, stillpreferably less than 50 nm, and still more preferably less than 30 nm.According to the invention the individual crystallites of the statedsizes are typically joined by sintering, forming an interconnected butporous network. In some cases, an average of at least 50% of the surfacearea of the primary crystallites is exposed so that it can contact theelectrolyte. To determine the percentage of exposed surface area, thefollowing procedure can be used: the average primary particle size andshape was measured, for instance by electron microscopy, and the surfacearea per unit mass can be thus computed. This would be the surface areathat would result for completely isolated particles. The specificsurface area of the powder can then be measured and compared to thefirst number. The latter should be at least 50% of the former. Inaccordance with having a very small primary crystallite size andaggregates that are not highly densified, the specific surface areas ofthe materials of the invention are preferably greater than about 10m²/g, more preferably greater than about 20 m²/g, more preferablygreater than about 30 m²/g, and still more preferably greater than about40 m²/g.

It is understood that olivines with other metals partially or completelysubstituted for Fe, including but not limited to LiMnPO₄ and LiCoPO₄, orothers in the family of polyanion compounds, including but not limitedto those with continuously joined networks of transition metal filledpolyhedra within the structure, may enjoy the benefits of improvedelectronic conductivity, reduced crystallite size, high reversiblecharge capacity, high rate capability, and other benefits describedherein when they are doped or processed according to the invention.

EXAMPLE 3 Electrode Fabrication and Electrochemical Tests

A composition Li_(0.998)Nb_(0.002)FePO₄ was prepared as described inexamples 1 and 2 using lithium carbonate, niobium phenoxide, ironoxalate, and ammonium dihydrogen phosphate, and heat treated accordingto the procedure labeled as HT1 shown in Table 2. The resulting powderwas black and conductive, and was cast as an electrode coating on analuminum foil current collector, using a standard formulation of 85 wt %of said composition, 10 wt % SUPER P™ carbon, and 5 wt % PVDF binder.γ-butyroactone was used as the solvent. The positive electrode (cathode)coating was tested against a lithium metal foil counterelectrode (anode)in a standard cell assembly using CELGARD® 2400 separator film andEC:DMC (+1M LiPF₆) as the electrolyte. Galvanostatic tests wereperformed at several current rates. FIG. 17A shows the firstelectrochemical cycle at C/30 rate, in which it is seen that a capacityof about 150 mA/g is obtained. A flat voltage plateau is observed,indicating a two-phase equilibrium of constant lithium chemicalpotential. FIG. 17B shows capacity vs. cycle number for this electrodeat a 1 C rate (150 mA/g), to about 260 cycles. FIG. 17C shows that thecoulombic efficiency vs. cycle number at 1 C rate (150 mA/g) isgenerally greater than about 0.997. These results show that thismaterial of the invention had good performance as a storage cathode forrechargeable lithium battery systems, at practical rates of charge anddischarge, without requiring special procedures, such as coating withconductive additives.

EXAMPLE 4 Electrode Fabrication and Electrochemical Tests of the LithiumStorage Compounds and Electrodes of the Invention at High DischargeRates

The electrochemical performance of the undoped and doped powders ofExamples 1 and 2 were evaluated by using them in electrodes of a varietyof formulations and testing said electrodes under a wide range ofconditions as the positive electrode in a liquid electrolyte cell, usinglithium metal foil as the negative electrode. Table 5 lists several ofthe electrode formulations that were prepared and tested. All sampleswere tested using CELGARD® 2400 or 2500 separator film and 1:1 EC:DECwith 1M LiPF₆ liquid electrolyte.

TABLE 5 Lithium Storage Materials and Electrode Formulations ActiveSpecific Material Active Materials Surface Electrode Loading Compositionand Area Formulation (mg/ Sample Heat Treatment (m²/g) (wt percentagescm²) A LiFePO₄, 700° C./Ar 3.9 Cathode/Super- 5.3 P/Kynar 461 79/10/11 BLiFePO₄, 700° C./Ar 3.9 Cathode/Super- 7.8 P/Kynar 461 79/10/11 C(Li_(0.99)Zr_(0.01))FePO₄, ~40 Cathode/Super- >3.9 600° C./ArP/Alfa-Aesar PVdF 78.3/10.1/11.6 D (Li_(0.99)Zr_(0.01))FePO₄, ~40Cathode/Super- 2.5 600° C./Ar P/Alfa-Aesar PVdF 78.4/10.0/11.6 E(Li_(0.99)Zr_(0.01))FePO₄, 41.8 Cathode/Super- 4.0 600° C./Ar P/Kynar2801 79/10/11 F (Li_(0.99)Zr_(0.01))FePO₄, 41.8 Cathode/Super- 4.3 600°C./Ar P/Kynar 2801 79/10/11 plasticized G (Li_(0.99)Zr_(0.01))FePO₄,41.8 Cathode/Super- 4.4 600° C./Ar P/Kynar 2801 79/10/11 plasticized H(Li_(0.99)Zr_(0.01))FePO₄, 26.4 Cathode/Super- 5.3 700° C./Ar P/Kynar461 79/10/11 I Li(Fe_(0.98)Ti_(0.02))PO₄, ~40 Cathode/Super- 5.9 600°C./Ar P/Kynar 461 79/10/11 J (Li_(0.998)Nb_(0.002))FePO₄, ~40Cathode/Super- — 600° C./Ar P/Alfa-Aesar PVdF 85/10/5Table 5, Sample D.

A composition (Li_(0.99)Zr_(0.01))FePO₄, fired at 600° C. in Araccording to the methods of Example 2, and having a specific surfacearea of about 40 m²/g, was formulated into an electrode by mixing 78.4wt % of the active material, 10.0 wt % of SUPER P™ carbon, and 11.6 wt %Alfa-Aesar PVdF as the binder, using γ-butyrolactone as solvent. Themixing was done in a small plastic container containing one Teflon® ballusing a dental amalgamator (Wig-L-Bug) for 5 minutes. Mixed suspensionswere cast onto aluminum foil current collectors, dried, and pressed at 4tons/cm². Electrochemical test samples were cut from the pressedcastings and assembled in stainless steel test cells with lithium metalfoil (Alfa Aesar, Ward Hill, Mass., USA) as the counterelectrode andCELGARD® 2400 (Hoechst Celanese, Charlotte, N.C., USA) as the separator.The liquid electrolyte used was 1:1 by wt ethylene carbonate and diethylcarbonate with 1M LiPF₆ added as the conductive salt.

FIG. 18A shows the charge and discharge capacities of a cell with about2.5 mg/cm² loading of the active material, observed in continuouscycling at rates varying from 15 mA/g (C/10) to 3225 mA/g (21.5 C)between the voltage limits of 2.8-4.2V, at room temperature. It is notedthat a stable capacity is obtained upon cycling over a wide range ofrates, to more than 150 cycles. FIG. 18B shows correspondingcharge-discharge curves for the doped sample, in which there is only amodest polarization, with a clear voltage plateaus at ˜3. 1V even at adischarge rate of 21.5 C. Comparing with published data for LiFePO₄, itis clear that the low doping levels used to increase conductivity andincrease specific surface area do not decrease the storage capacity atlow rates, but greatly increase the power density that is possible. Thelow polarization is attributed to the high electronic conductivity atthe particle scale. Thus this electrode made using a compound of theinvention is seen to have high energy density at much higher currentrates than previously seen for undoped LiFePO₄.

Table 5, Sample C.

An electrode prepared as described for Sample D of Table 5, andhaving >3.9 mg/cm² loading of active material, was assembled in aTeflon® and stainless steel Swagelok® test vessel with lithium metalfoil (Alfa Aesar, Ward Hill, Mass., USA) as the counterelectrode andCELGARD® 2400 (Hoechst Celanese, Charlotte, N.C., USA) as separator. Theliquid electrolyte used was 1:1 by wt ethylene carbonate and diethylcarbonate with 1M LiPF₆ added as the conductive salt.

FIG. 19A shows discharge capacities measured at 42° C. observed incontinuous cycling tests. For the curve labeled 0.2 C, the cell wascharged and discharged at a current rate of 0.2 C (30 mA/g) between thevoltage limits of 2-4.2V. For the other curves, the cell was charged ata rate of 1.1 C (165 mA/g) and then discharged at the rates shown. It isseen that this cell maintains a significant discharge capacity andrelatively little polarization upon discharging at rates as high as 66.2C (9.93 A/g). Compared to previously reported electrochemical test datafor LiFePO₄, this cell can be discharged at a remarkably high powerdensity while still having significant energy density.

Table 5, Sample F, E, G, H.

Sample F was prepared from a composition (Li_(0.99)Zr_(0.01))FePO₄,fired at 600° C. in Ar according to the methods of Example 2, and havinga specific surface area of 41.8 m²/g. It was formulated into anelectrode by mixing 79 wt % of the active material, 10 wt % of SUPER P™carbon, and 11 wt % Kynar 2801 binder in γ-butyrolactone as solvent,using the procedures of Sample D and C. After casting and drying, thecoating was immersed in a plasticizing solvent of 15 wt % propylenecarbonate in methanol, then pressed and dried. The resulting positiveelectrode (cathode) was tested against a lithium metal foilcounterelectrode (anode) in a Swagelok cell assembly using CELGARD® 2500separator film and 1:1 EC:DEC with 1M LiPF₆ liquid electrolyte.

FIG. 20 shows discharge curves for this cell measured by theconstant-current constant-voltage (CCCV) method whereby the cell wasfirst charged at 0.5 C rate (75 mA/g), then held at the upper limitingvoltage of 3.8V until the charging current decayed to 0.001 mA, beforedischarging to 2V at the stated rate. Note that in comparison to FIG.19, the initial linear behavior upon discharge is not seen, indicatingthat the linear region is a capacitive response due to incompleteequilibration in the cell. (In later calculations of the energy densityof cell tested in continuous cycling, the capacity of this linear regionis not included.) The results in FIG. 20 show quite remarkably that evenat a 50 C (7.5 A/g) discharge rate, about half of the capacity availableat C/5 rate is provided by the cell.

FIG. 21 compares the discharge energy density of Sample F with SamplesE, G, and H from Table 5. All tests were conducted at 22-23° C. Sample Gwas prepared in the same manner as Sample F, and was tested bycontinuous cycling according to the procedure of Sample C. Sample E wasprepared and tested in the same manner as Sample G, except that theelectrode was not plasticized. Sample H was prepared from a powder firedto a higher temperature than the others in FIG. 21, 700 C in Ar, and hasa lower specific surface area of 26.4 m²/g, and used Kynar 461 binder,but was otherwise processed and tested in like manner. It is seen thatall four of the samples in FIG. 21 exhibit a remarkably high capacity athigh discharge C rates.

Table 5, Samples A and B

Samples A and B were prepared from undoped LiFePO₄, which after firingat 700 C has a relatively low specific surface area of 3.9 m²/g. Theelectrodes were prepared and tested in like manner to Sample H in Table5, and the results are shown in FIG. 22, measured at 23, 31, and 42° C.Unlike the results in FIG. 21, however, the undoped samples show greatlyinferior discharge capacity that falls to about 20 mAh/g by about 5 C(750 mA/g) rate. It is also seen in FIG. 22 that heating to atemperature of 42° C. does not significantly improve the dischargecapacity.

Comparison with Literature Data

Electrochemical test results have been reported for severalLiFePO₄-based electrodes in the published literature. FIG. 23 comparesthe results from Sample F in Table 5 to results from several publishedpapers. It is seen that the electrodes of the invention have markedlyhigher discharge capacity at high rates, whereas the literature datatypically shows a rapid decrease in capacity with increasing rate atrates below 5 C or 10 C rate. This comparison illustrates the novel highperformance properties of the lithium storage materials and electrodesof the current invention.

Energy Density vs. Current Density

In FIGS. 24-27, we show the discharge energy density available from thetotal mass of storage compound available in several electrodes of Table5, plotted against the current per gram of storage material. The energydensities are obtained by integrating the voltage vs. charge capacitycurves. In FIG. 24, results from Sample F are shown for a measurementtemperature of 22° C.; in FIG. 25, results for Sample G are shown formeasurement temperatures of 23, 31, and 42° C.; in FIG. 26, results forSample I measured at 23° C.; and in FIG. 27, results are shown forSample A for measurement temperatures of 23, 31, and 42° C. ComparingFIGS. 24-26 with FIG. 27, the vast improvement in the energy density ofthe lithium storage materials of the invention compared to undopedLiFePO₄ is clearly seen

EXAMPLE 5 Storage Battery Cells

Example 4 illustrates the high discharge capacity available from thelithium storage compounds of the invention, and electrodes utilizingsaid compounds, at high discharge rates. Having shown clearly theimproved electrochemical properties of the lithium storage compounds andelectrodes of the invention, we now illustrate storage battery cells ofexceptional power density and high energy density based on thesecompounds and electrodes.

It is well-known that typical lithium-ion batteries based on laminatedelectrodes and designed for high energy density contain 25-35% by weightand 13-18% by volume of the positive electrode storage compound,typically LiCoO₂. While more detailed calculations of the weight andvolume fractions of materials are used for specific designs, theseapproximate values provide an adequate basis for determining the energydensity and power density of conventional cell designs utilizing thepresent lithium storage compounds. Accounting for the 29% lower crystaldensity of LiFePO₄ compared to LiCoO₂, and assuming a somewhat lowerpacking density due to the high specific surface area, it isconservatively estimated that an optimized cell could contain 10-20 wt %of the positive electrode active material. Using the results of Example4 for electrodes tested against lithium metal negative electrodes, andtaking into account its slightly lower cell voltage when used inconjunction with a carbon electrode (3.25 vs. 3.7 V), the powerdensity—energy density results shown in FIG. 28 are obtained. Resultsare shown for 10 wt %, 15 wt %, and 20 wt % of the positive electrodeactive material. Power and energy densities for complete discharge of acell of 800-1500 W/kg and 30-60 Wh/kg at a 20 C (3 A/g) rate, 1500-4200W/kg and 15-30 Wh/kg at a 50 C (7.5 A/g) rate, and 2500-5000 W/kg and5-10 Wh/kg at a 80 C (12 A/g) rate, are obtained. Such cells couldprovide power densities not possible in current nickel metal-hydride(400-1200 W/kg, 40-80 Wh/kg) and lithium-ion battery technology(800-2000 W/kg, 80-170 Wh/kg). These capabilities, in a low-cost andultra-safe storage material, may be especially attractive for high powerand large battery applications including but not limited to power toolsand hybrid and electric vehicles.

EXAMPLE 6 Doping From Milling Media and Containers

This example shows that doping to yield high electronic conductivity canbe accomplished by using suitable milling media and containers. It alsoshows that the high electronic conductivity of the materials of theinvention is obtained without excessive carbon or other conductiveadditives. Table 6 shows the results of carbon and zirconium analysis ofseveral materials prepared according to the methods of Examples 1 and 2.It is seen that milling with ⅜″ ZrO₂ milling media can add a detectableconcentration of Zr to the samples. Amongst the nominally undopedsamples, a high conductivity of about 10⁻³ S/cm is observed when the Zrconcentration from the milling media is 0.018. Taking this added Zr intoaccount, the composition of the sample is of type Li_(1−a) Zr_(a)FePO₄,similar to other high conductivity samples. It is also seen that thepolypropylene milling jar has added some excess carbon to this sample.When ¼″ ZrO₂ milling media are used, negligible Zr doping occurs. Anundoped sample fired at 800 C has 0.25 wt % carbon, and a lowconductivity of 10⁻⁸ S/cm.

Lightly doped samples such as in Table 1 that have been milled withzirconia milling media can thus also be doped with Zr in addition,improving the conductivity.

The four Zr and Nb doped samples, were formulated to haveLi_(1−a)M″_(a)FePO₄ composition and have high electronic conductivity.The concentration of carbon is less than 2 weight percent in oneinstance, and less than 1 weight percent in the other three instances.The sample of highest conductivity, 10⁻² S/cm, has the lowest carbonconcentration, only 0.32 weight percent, nearly the same as the highlyinsulating undoped samples. The sample with the highest carbonconcentration has the lowest conductivity. These results show that thehigh electronic conductivity of doped samples is not correlated withcarbon concentration but instead with doping as described herein.

TABLE 6 Carbon analysis of conductive lithium iron phosphate materials.Conductivity Carbon Zr 2-probe Composition Preparation Method (wt %) (wt%) (S/cm) Undoped Polypropylene bottle, 0.25 0.009 10⁻¹⁰ (large batch)⅜″ ZrO₂ media 700° C. Undoped Polypropylene bottle, 2.41 0.018 (~10⁻³) (Li_(0.99)FePO₄) ⅜″ ZrO₂ media 700° C. Undoped Porcelain jar, 0.25 10⁻⁸800° C. ¼″ ZrO₂ media 1% Zr doped Porcelain jar, 1.46 10⁻⁴ 700° C. ¼″ZrO₂ balls 1% Zr doped Porcelain jar, 0.86 10⁻³ 800° C. ¼″ ZrO₂ balls 1%Nb doped Porcelain jar, 0.56 10⁻³ 800° C. Tiny ZrO₂ balls 1% Nb dopedPolypropylene bottle, 0.32 10⁻² 800° C. ⅜″ ZrO₂ media

EXAMPLE 7 Compositions with Dopant not in Solid Solution

In this example, as in Example 1, it is shown that when a dopedcomposition similar to the preceding examples of high electronicconductivity is prepared, but the dopant is not in solid solution, thenthe composition is not conductive. In Example 2, it was shown that acomposition (Li_(0.99)Nb_(0.01))FePO₄ has markedly improved conductivityand electrochemical storage properties compared to an undoped LiFePO₄when the Nb dopant is in solid solution in the crystal lattice. Here itis shown that the same composition prepared with the dopant not in solidsolution, but precipitated as a secondary phase, is substantiallyinsulating.

1 mole % Nb-doped LiFePO₄ was prepared using iron acetate, Fe(CH₃COO)₂as the Fe precursor. Niobium phenoxide, Nb(C₆H₅O)₅ was used as thesource of the dopant. The theoretical content of Fe in iron acetate is32.12 wt %. However, the iron content of iron acetate frequentlydeviates from the ideal value. Thus it was expected that the compositionof the compound would deviate from a nominal composition(Li_(0.99)Nb_(0.01))FePO₄ that provides good electronic conductivity. Abatch of powder was formulated according to the following proportions ofstarting materials:

1 mole % Nb-doped LiFePO₄ ~4 g batch NH₄H₂PO₄ 2.3006 g (99.998%,Alfa-Aesar) Li₂CO₃ 0.7316 g (99.999%, Alfa-Aesar) Fe(CH₃COO)₂ 3.7867 g(99.9%, Alfa-Aesar) Nb(C₆H₅O)₅ 0.1116 g (Alfa-Aesar)

Each of the components was weighed in an argon-filled glove box. Theywere then removed from the glove box and ball milled, using zirconiamilling balls (˜¼″ diameter, 400-450 g total weight) in a porcelainmilling jar (300 ml capacity) for 24 hours in acetone (150-160 ml) at230 rpm. The milled mixture was dried at a temperature not exceeding 80°C., and then ground with a mortar and pestle in the argon-filled glovebox. The mixture was then heat treated in two steps. A first heattreatment at 350° C. for 10 hours was conducted in a flowing Ar (99.999%purity) atmosphere (>400 cc/min). The powder sample was then ground inlaboratory air atmosphere, using a mortar and pestle, and subjected to asecond heat treatment at a higher temperature (600° C. to 700° C.) for20 hours, in flowing Ar gas (>400 cc/min). The heating and cooling ratesfor each step were 5° C./min. Before heating, purging of the furnacetube in flowing Ar for about 1 hour was conducted.

In contrast to the cases where iron oxalate (FeC₂O₄.2H₂O) is used as thestarting materials, a 2-probe resistance measurement of this sampleshowed that the conductivity is less than 10⁻⁷ S/cm at a temperature of23-27° C. X-ray diffraction of a sample fired at 600 C for 20 h in Arshowed that it was predominantly LiFePO4 but had a small amount of anunidentified secondary phase. TEM analysis showed that the dopant Nb wasnot detectable inside the particles, but was segregated as a secondaryphase. Furthermore, the specific surface area of this material was muchlower than it is in samples prepared so that the Nb dopant is in solidsolution, being 14.3 m²/g for 600 C firing. Thus it is shown that inthis material, when a substantial amount of the added Nb dopant is notin solid solution in the crystalline particles, an increasedconductivity is not observed, nor is the advantageous feature of metaladditives of diminishing the crystallite size realized. It is understoodthat the iron acetate precursor, being a suitable reactant for theformation of LiFePO₄, is suitable for producing highly conductivecompositions when the overall composition is known and more preciselycontrolled.

EXAMPLE 8 Solid State Reaction Synthesis of LiFePO₄

This example describes the preparation of LiFePO₄, using wustite ironoxide, FeO, and lithium metaphosphate, LiPO₃, as precursors. Anadvantage of these precursors is that they form a closed or nearlyclosed reaction system, by which it is meant that upon heat treatment,few if any gaseous species are produced as a reaction by product.Adjustments to the relative amounts of the reactants, and the additionof other constituents such as the dopants in the form of oxides can beused in order to obtain compositions comprising the materials of theinvention.

A batch of 6 g LiFePO₄ was prepared by using starting materials of thefollowing amounts: 2.733 g FeO (99.5%, Alfa-Aesar, Ward Hill, Mass.,USA) and 3.267 g LiPO₃ (97%, City Chemical LLC., West Haven, Conn.,USA). The components were weighed in an Ar-filled glove box, andtransferred to a porcelain jar and ball-milled in acetone for 48 h usingzirconia milling balls. The acetone was evaporated from the milledpowder at a low temperature (<100° C.), and the dried powder was groundwith a mortar and pestle and pressed into pellets. The pellets wereembedded in loose powder of the same material and placed in aluminacrucibles and subjected to a single heat treatment under Ar atmosphereat 550-900° C. for 20 h.

The heat-treated samples were light to medium grey in color.Predominantly single-phase LiFePO₄ was obtained for all heat-treatmenttemperatures, as identified by X-ray diffraction. Minor amounts of Fe₂Pand Fe phases were detected by XRD at heat-treatment temperatures at andabove 600° C.

EXAMPLE 9 Solid State Reaction Synthesis of Nb-doped LiFePO₄

Conductive compositions of the invention are obtained using the startingmaterials and basic procedure of Example 8, and by adding dopants in theform of oxides, hydroxides or alkoxides to obtain the dopant metal ionin the preferred valence state. A conductive sample with the nominalformulation LiFePO₄+1 mole % Nb was prepared using the precursors ofExample 8 and adding a small amount of the dopant niobium phenoxide,Nb(C₆H₅O)₅. A batch of about 1 g powder was prepared by using 0.4530 gFeO, 0.5416 g LiPO₃ and 0.0352 g Nb(C₆H₅O)₅ (99.99%, Alfa-Aesar, WardHill, Mass., USA). The powders were milled, as described in Example 6,and then pressed into pellets and heat-treated under Ar atmosphere at600° C. for 20 h. Some sintered pellets were also annealed at 850° C. toobtain more densified samples or samples with more coarsenedcrystallites.

In contrast to the undoped powder of Example 8, the resulting powder wasdark grey in color, which gave an indication of increased electronicconductivity, compared to the undoped sample. X-ray diffraction analysisshowed predominantly a single crystalline phase of the triphyliteLiFePO₄ structure. Resistance measurements were made using a two-contactmethod with metal probes located about 5 mm apart on the fired pellets,and showed a resistivity of about 150 kΩ, in contrast to the insulatingsample of Example 8, which when made by the same procedure and from thesame starting materials except for the absence of doping with niobiumphenoxide showed a resistance of >200 mega ohms (MΩ). Thus it is shownthat the doped compositions of the invention prepared according to themethods of this example provide an increased electronic conductivitycompared to an undoped composition.

EXAMPLE 10 Solid State Reaction Synthesis of Conductive LiFePO₄

In this example, doped LiFePO₄ with increased electronic conductivity isprepared using the starting materials and methods of Example 8 and 9,except that the conductive compositions of the invention are obtained byadding dopants in the form of oxides wherein the dopant are in thepreferred final valence state, including but not limited to TiO₂, Nb₂O₅,Ta₂O₅, ZrO₂, Al₂O₃, MgO, or WO₆. The dopant oxide is added to thestarting mixture of reactants in a quantity sufficient to give a desiredconcentration in the final product. Using the mixing and firingprocedures of Examples 8 and 9, conductive compositions of the inventionare obtained.

EXAMPLE 11 Solid-state Reaction Synthesis

This example describes the all-solid state reaction synthesis of LiFePO₄or conductive doped LiFePO₄, using wustite iron oxide, FeO, lithiumoxide, Li₂O, and phosphorous(V) oxide, P₂O₅, as precursors to the majormetallic constituents and metal alkoxides and metal oxides as the sourceof the dopants. This set of precursors also forms a closed or nearlyclosed reaction system, from which few if any gaseous species areevolved during synthesis.

A batch of 12 g LiFePO₄ was prepared by using starting materials of thefollowing amounts: 5.463 g FeO (99.5%, Alfa-Aesar, Ward Hill, Mass.,USA), 1.136 g Li₂O (99.5%, Alfa-Aesar, Ward Hill, Mass., USA) and 5.398g P₂O₅ (99.99%, Alfa-Aesar, Ward Hill, Mass., USA). The components wereweighed in an Ar-filled glove box, transferred to a polypropylene jarand ball-milled for 48 h using zirconia milling balls. Specialprecautions were taken to avoid any exposure of the reactant mixture toair, due to the very hygroscopic nature of P₂O₅. For instance, a liquidmilling medium (e.g. acetone) was not added prior to milling. The dry,milled powder was extracted from the milling jar in the glove box,ground with mortar and pestle and pressed into pellets. The pellets wereplaced in alumina crucibles and subjected to a single heat treatment at550° C. or 850° C. for 20 h., after which the samples were found byX-ray diffraction to contain LiFePO₄ as the major crystalline phase.Doped samples are prepared in the same manner, except with the additionof a dopant salt such as a metal alkoxide or metal oxide prior to themixing and milling steps.

EXAMPLE 12 Solid-state Reaction Synthesis

This example describes the preparation of undoped or doped LiFePO₄,using iron oxalate, FeC₂O₄.2H₂O, and lithium metaphosphate, LiPO₃, asprecursors. Gaseous species formed during synthesis are limited to oneformula unit carbon dioxide CO₂, one formula unit carbon monoxide CO andtwo formula units water H₂O per formula unit reacted FeC₂O₄.2H₂O.

A batch of 1 g LiFePO₄ was prepared by using starting materials of thefollowing amounts: 1.134 g FeC₂O₄.2H₂O (99.99%, Aldrich, Milwaukee,Wis., USA) and 0.5410 g LiPO₃ (97%, City Chemical LLC., West Haven,Conn., USA). The components were weighed in an Ar-filled glove box, andball milled in acetone in a porcelain jar for about 24 h, using zirconiamilling balls. The acetone was evaporated from the milled powder at alow temperature (<100° C.), and the dried powder was ground using amortar and pestle. The milled powder was heat treated at 350° C. for 10h under flowing Ar gas. The heat-treated powder samples were then groundagain with a mortar and pestle and pressed into pellets before a secondheat-treatment step. The pellets were placed in alumina crucibles andheated to 600° C. or 700° C. for 20 h under Ar gas. X-ray diffractionshowed that a predominantly single-phase LiFePO₄ was obtained for bothheat-treatment temperatures. A minor amount of another detectable phase(2θ˜ 27, 28, 30 and 31°) was also observed. Doped samples are preparedin the same manner, except with the addition of a dopant salt prior tomixing and milling.

EXAMPLE 13 Solid-state Reaction Synthesis

This example describes the preparation of undoped or doped LiFePO₄,using iron oxalate, FeC₂O₄.2H₂O, lithium oxide, Li₂O, and phosphorous(V)oxide, P₂O₅, as precursors. The formation of gaseous species duringsynthesis is limited to one formula unit carbon dioxide CO₂, one formulaunit carbon monoxide CO and two formula units water H₂O per formula unitreacted FeC₂O₄.2H₂O.

A batch of 1 g LiFePO₄ was prepared by using starting materials of thefollowing amounts: 1.134 g FeC₂O₄.2H₂O (99.99%, Aldrich, Milwaukee,Wis., USA), 0.09421 g Li₂O (99.5%, Alfa-Aesar, Ward Hill, Mass., USA)and 0.4475 g P₂O₅ (99.99%, Alfa-Aesar, Ward Hill, Mass., USA). Thecomponents were weighed in an Ar-filled glove box, and dry-milled in aporcelain jar for about 24 h using zirconia milling balls. The milledpowder was extracted from the milling jar in the glove box and groundusing a mortar and pestle. The powder was then heat treated at 300° C.for 10 h under flowing Ar gas, ground again and pressed into pelletsbefore a second heat treatment step. The pellets were placed in aluminacrucibles and heated to 600° C. or 700° C. for 20 h under Ar gas. X-raydiffraction showed a predominantly single-phase LiFePO₄ for bothheat-treatment temperatures. A minor amount of another detectable phase(2θ˜ 27 and 28°) and possibly a minor amount of Fe₃O₄ was also observed.Doped samples are prepared in the same manner, except with the additionof a dopant salt prior to mixing and milling.

EXAMPLE 14 Chemically Delithiated Doped Conductive LiFePO₄

This example describes the chemical delithiation of a doped andconductive LiFePO₄, after which it remains highly electronicallyconductive as predominantly an FePO₄ phase. The chemical reduction ofLiFePO₄ was conducted by the addition of a strong reducing agent, inthis case nitronium hexafluorophosphate, NO₂PF₆, to a suspension of thestarting material and acetonitrile, CH₃CN. Nitrogen dioxide gas, NO₂,and solvated lithium hexafluorophosphate, LiPF₆, is formed during thereaction together with the reduced FePO₄, according to:LiFePO₄(s)+NO₂PF₆(sol.)→NO₂(g)+LiPF₆(sol.)+FePO₄(s)(sol.=solvated)

Specifically a powder of (Li_(0.99)Nb_(0.01)) FePO₄ was delithiated. Toobtain a relatively complete level of delithiation, the molar ratioNO₂PF₆: (Li_(0.99)Nb_(0.01)) FePO₄ was set to 2:1. For a batch of 0.6 g(Li_(0.99)Nb_(0.01)) FePO₄ (prepared according to Example 2), an amountof 1.453 g of NO₂PF₆ (98%, Matrix Scientific, Columbia, S.C., USA) wasused. Both reactants were weighed in an Ar-filled glove box andtransferred to a filtering flask equipped with a rubber stopper. A thinglass tube was fitted through a hole in the rubber stopper and asilicone tube was fitted to the tubulation opening on the flask side.100 ml of acetonitrile (99.998%, anhydrous, Alfa-Aesar, Ward Hill,Mass., USA) was added to the beaker, and the glass tube was adjusted sothat the tip was positioned under the liquid surface. The resultingconcentration of NO₂PF₆ in the solution was ca. 0.08 M. A flow of Ar gaswas introduced at the glass tube end, so that the gaseous species formedduring the reaction were led away through the silicone tube to anexhaust hood. The reaction was allowed to proceed for 24 h, whilestirring with a magnetic stirrer. The resulting powder was separatedfrom the solution by filtering through a Büchner funnel equipped withfilter paper (#595, Schleicher & Schuell). The powder was thoroughlyrinsed in pure acetonitrile and dried under vacuum for two hours. Theremaining powder was analysed by X-ray diffraction and showed asingle-phase orthorhombic FePO₄ structure. The powder was black incolor, and when pressed into a pellet, was highly conductive. Thus thisexample shows that the compounds of the invention remain highlyelectronically conductive upon delithiation, and that a partiallydelithiated compound comprises two phases, one relatively highlydelithiated and the other relatively delithiated, both of which areelectronically conductive.

Those skilled in the art would readily appreciate that all parametersand configurations described herein are meant to be exemplary and thatactual parameters and configurations will depend upon the specificapplication for which the systems and methods of the present inventionare used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific embodiments of the invention described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, the invention may be practiced otherwise thanas specifically described. Accordingly, those skilled in the art wouldrecognize that the use of an electrochemical device in the examplesshould not be limited as such. The present invention is directed to eachindividual feature, system, or method described herein. In addition, anycombination of two or more such features, systems or methods, if suchfeatures, systems or methods are not mutually inconsistent, is includedwithin the scope of the present invention.

What is claimed is:
 1. A composition comprising a compound selected fromthe group consisting of (Li_(1−a)M″_(a))_(x)M′(PO₄) and(Li_(b−a)M″_(a))_(x)M′(PO₄), wherein M′ is a first-row transition metal,M″ is one or more dopants selected from a Group IIA, IIIA, IVA, VA, VIA,VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, 0.0001<a≦0.1, a≦b≦1,and x is greater than zero, wherein (i) the composition has a specificsurface area of at least 15 m²/g; (ii) the composition crystallizes inan ordered or partially disordered structure of the olivine Li_(x)M(PO₄)structure type; and (iii) M″ is an ion selected to be supervalent to thelowest valence state of M′ in the compound; and additionally having amolar concentration of the metals (M′+M″) relative to the concentrationof P that exceeds the ideal stoichiometric ratio of 1:1 in the olivinestructure type compound by at least 0.0001.
 2. A composition comprisinga compound Li_(x)(M′_(1−a)M″_(a))PO₄, wherein M′ is a first-rowtransition metal, M″ is one or more dopants selected from a Group IIIA,IVA, VA, VIA, VIIA, VIIIA, IB, IIIB, VB, and VIB metal, 0.0001<a≦0.1,and x is greater than zero, wherein (i) the composition has a specificsurface area of at least 15 m²/g; (ii) the composition crystallizes inan ordered or partially disordered structure of the olivine Li_(x)M(PO₄)structure type; and (iii) M″ is an ion selected to be supervalent to thelowest valence state of M′ in the compound.
 3. The composition of claim1, wherein the molar concentration of the metals (M′+M″) relative to theconcentration of P exceeds the ideal stoichiometric ratio of 1:1 in ofthe olivine structure type compound by at least 0.01.
 4. The compositionof claim 1, wherein the molar concentration of the metals (M′+M″)relative to the concentration of P exceeds the ideal stoichiometricratio of 1:1 in of the olivine structure type compound by at least0.002.
 5. The composition of claim 1, wherein the molar concentration ofthe metals (M′+M″) relative to the concentration of P that exceeds theideal stoichiometric ratio of 1:1 in of the olivine structure typecompound by an amount in the range of 0.001 to 0.04.
 6. The compositionof claim 1 or 2, wherein M′ is a first row transition metals selectedfrom the group consisting of iron, vanadium, chromium, manganese, cobaltand nickel and the mixture thereof.
 7. The composition of claim 6,wherein M′ is Fe²⁺.
 8. The composition of claim 7, wherein M′ furthercomprises an additional first-row transition metal.
 9. The compositionof claim 1, wherein M″ is any of one or more dopants selected fromaluminum, titanium, zirconium, niobium, tantalum, tungsten, or magnesiumor combinations thereof.
 10. The composition of claim 2, wherein M″ isany of one or more dopants selected from aluminum, titanium, zirconium,niobium, tantalum, tungsten, and combinations thereof.
 11. Thecomposition of claims 1 or 2, wherein the compound, upon delithiation,undergoes phase-separation into a substantially lithiated compound and asubstantially delithiated compound, each of which has an electronicconductivity of at least 10⁻⁶ S/cm.
 12. The composition of claims 1 or2, wherein the composition contains in crystalline solid solution,amongst the metals M′ and M″, simultaneously the metal ions Fe²⁺ andFe³⁺, Mn²⁺ and Mn³⁺, Co²⁺ and Co³⁺, Ni²⁺ and Ni³⁺, V²⁺ and V³⁺, or Cr²⁺and Cr³⁺, with the ion of lesser concentration being at least 10 partsper million of the sum of the two ion concentrations.
 13. Thecomposition of claims 1 or 2, wherein the M″ includes a metal with ionicradius less than the average ionic radius of the M′ ions.
 14. Thecomposition of claims 1 or 2, wherein vacancy defects are present on alattice site.
 15. The composition of claims 1 or 2, wherein lithium issubstituted onto a M2 site of a crystal of the composition at aconcentration of at least 10¹⁸ per cubic centimeter, or x and a areselected such that lithium can substitute into an M2 site of a crystalof the composition as an acceptor defect.
 16. The composition of claims1 or 2, wherein the composition compound is Li_(x)vac_(y)(M¹_(−a)M″_(a))PO₄, Li_(x−ay)M″_(a)vac_(y)M′PO₄,Li_(x)(M′_(1−a−y)M″_(a)vac_(y))PO₄ or Li_(x−a)M″_(a)M′_(1−y)vac_(y)PO₄,wherein vac represents a vacancy in a structure of the compound.
 17. Thecomposition of claim 16, wherein M′ is Fe.
 18. The composition of claims1 or 2, wherein M″ has a concentration of at least 0.01 atom % relativeto the concentration of M′.
 19. The composition of claims 1 or 2,wherein M″ has a concentration of at least 0.02 mole % relative to theconcentration of M′.
 20. The composition of claims 1 or 2, wherein M″has a concentration of at least 0.05 mole % relative to theconcentration of M′.
 21. The composition of claims 1 or 2, wherein M″has a concentration of at least 0.1 mole % relative to the concentrationof M′.
 22. The composition of claims 1 or 2, wherein the compound has aspecific surface area of at least 20 m²/g.
 23. The composition of claims1 or 2, wherein the compound has a specific surface area of at least 30m²/g.
 24. The composition of claims 1 or 2, wherein the compound has aspecific surface area of at least 40 m²/g.
 25. The composition of claims1 or 2, wherein the compound has a specific surface area of at least 50m²/g.
 26. The composition of claims 1 or 2, wherein the conductivity isat least 10⁻⁷ S/cm.
 27. The composition of claims 1 or 2, wherein theconductivity is at least 10⁻⁶ S/cm.
 28. The composition of claims 1 or2, wherein the conductivity is at least 10⁻⁵ S/cm.
 29. The compositionof claims 1 or 2, wherein the conductivity is at least 10⁻⁴ S/cm. 30.The composition of claims 1 or 2, wherein the conductivity is at least10⁻³ S/cm.
 31. The composition of claims 1 or 2, wherein theconductivity is at least 10⁻² S/cm.
 32. An electrode comprising thecomposition of claims 1 or 2 as a storage material.
 33. The electrode ofclaim 32, having a material energy density that while: charging ordischarging at a rate ≧30 mA per g of storage compound, is greater than350 Wh/kg, or charging or discharging at a rate ≧150 mA per g of storagecompound, is greater than 280 Wh/kg, or charging or discharging at arate ≧300 mA per g of storage compound, is greater than 270 Wh/kg, orcharging or discharging at a rate ≧750 mA per g of storage compound, isgreater than 250 Wh/kg, or charging or discharging at a rate ≧1.5 A perg of storage compound, is greater than 180 Wh/kg, or charging ordischarging at a rate ≧3 A per g of storage compound, is greater than 40Wh/kg, or charging or discharging at a rate ≧4.5 A per g of storagecompound, is greater than 10 Wh/kg.
 34. The electrode of claim 32,having a material energy density that while: charging or discharging ata rate ≧30 mA per g of storage compound, is greater than 420 Wh/kg, orcharging or discharging at a rate ≧150 mA per g of storage compound, isgreater than 400 Wh/kg, or charging or discharging at a rate ≧300 mA perg of storage compound, is greater than 370 Wh/kg, or charging ordischarging at a rate ≧750 mA per g of storage compound, is greater than350 Wh/kg, or charging or discharging at a rate ≧1.5 A per g of storagecompound, is greater than 270 Wh/kg, or charging or discharging at arate ≧3 A per g of storage compound, is greater than 150 Wh/kg, orcharging or discharging at a rate ≧4.5 A per g of storage compound, isgreater than 80 Wh/kg, or charging or discharging at a rate ≧6 A per gof storage compound, is greater than 35 Wh/kg, or charging ordischarging at a rate ≧7.5 A per g of storage compound, is greater than50 Wh/kg, or charging or discharging at a rate ≧15 A per g of storagecompound, is greater than 10 Wh/kg.
 35. The electrode of claim 32,having a material energy density that while: charging or discharging ata rate ≧30 mA per g of storage compound, is greater than 475 Wh/kg, orcharging or discharging at a rate ≧150 mA per g of storage compound, isgreater than 450 Wh/kg, or charging or discharging at a rate ≧300 mA perg of storage compound, is greater than 430 Wh/kg, or charging ordischarging at a rate ≧750 mA per g of storage compound, is greater than390 Wh/kg, or charging or discharging at a rate ≧1.5 A per g of storagecompound, is greater than 350 Wh/kg, or charging or discharging at arate ≧3 A per g of storage compound, is greater than 300 Wh/kg, orcharging or discharging at a rate ≧4.5 A per g of storage compound, isgreater than 250 Wh/kg, or charging or discharging at a rate ≧7.5 A perg of storage compound, is greater than 150 Wh/kg, or charging ordischarging at a rate ≧11 A per g of storage compound, is greater than50 Wh/kg, or charging or discharging at a rate ≧15 A per g of storagecompound, is greater than 30 Wh/kg.
 36. The electrode of claim 32,wherein the electrode is a sheet or mesh of electronically conductivematerial coated with a loading of 4 mg to 20 mg of said storage compoundper square centimeter of projected area of the sheet or mesh.
 37. Theelectrode of claim 32, wherein said electrode is a sheet or mesh ofelectronically conductive material coated with said storage material andhas a total thickness of 20 micrometers to 200 micrometers.
 38. Theelectrode of claim 32, wherein M′ includes Fe²⁺.
 39. The electrode ofclaim 32 wherein M′ further comprises an additional first-row transitionmetal.
 40. A battery cell comprising: a positive electrode; a negativeelectrode; and a separator positioned between the positive electrode andthe negative electrode, wherein at least one of the positive electrodeor negative electrode comprises the composition of claims 1 or
 2. 41.The battery cell of claim 40, wherein the cell is incorporated intodisposable battery or a rechargeable battery.